Analytical Biochemistry

Fluorescent capillary gel electrophoresis (CGE) with sodium dodecyl sulfate (CE-SDS) provides a powerful, high-sensitivity alternative to ultraviolet (UV)-based detection for characterizing therapeutic monoclonal antibodies (mAb). Regulatory and standards organizations, such as the United States Pharmacopeia (USP), include only UV based CE-SDS methods, hindering adoption, of alternative detection methods. There is growing opportunity to expand beyond exclusively UV-based CE-SDS methods. In this study, we present a full analytical validation of a light-emitting diode (LED) fluorescence-based parallel CE-SDS method for both non-reduced and reduced analysis of therapeutic antibodies. Using the NISTmAb reference material as a model system, size heterogeneity critical quality attributes (CQAs) including monomeric purity, percent glycosylation, and percent thioether were assessed. The fluorescence method demonstrated high specificity and precision with relative standard deviation (RSD) values <1% for monomeric purity and glycosylation, and <3% for thioether), as well as robust performance across variations in injection voltage, electrophoresis voltage, labeling temperature, and Labeling Buffer concentration. Ruggedness testing across users and reagent lots confirmed reproducibility, and accuracy assessments showed strong agreement with reported values from the National Institute of Standards (NIST) and traditional UV detection measurements. Linearity studies yielded coefficient of determination (R2) values >0.995 for both non-reduced and reduced analyses. These results highlight the high sensitivity, stable baseline performance, and suitability of LED fluorescence-based parallel CE-SDS as a validated, higher-throughput alternative to traditional UV-based methods for mAb quality control (QC).

RNA modification analysis by LC-MS/MS is central to epitranscriptomics, yet quantitative comparison across laboratories and instrument platforms remains poorly standardized. Here, we performed a community-driven benchmarking study during the first Human RNome Project workshop to systematically evaluate cross-platform reproducibility of ribonucleoside mass spectrometry workflows. Using the same analytical column and gradient, standardized RNA samples, and shared reagents, we compared nucleoside quantification across quadrupole, time-of-flight, and orbitrap-based LC-MS platforms employing distinct acquisition strategies. While chromatographic separation was highly reproducible across systems, nucleoside-specific MS response behavior differed substantially between platforms and limited direct comparability of relative signal intensities. These response differences varied across analytes and concentration ranges, demonstrating that harmonized chromatography alone is insufficient for transferable quantitative analysis. Stable isotope-labeled internal standard (SILIS) normalization substantially reduced platform-and method-dependent response and improved agreement for most evaluated modifications. External calibration improved agreement between qTOF and Orbitrap workflows for a subset of modifications but did not fully resolve residual intersystem differences. Based on these findings, we establish benchmark-derived recommendations for harmonized relative and absolute RNA modification quantification, including guidance for calibration design, quality control, and data reporting. Together, this work provides a methodological framework for reproducible nucleoside LC-MS/MS workflows and establishes a foundation for large-scale comparative epitranscriptomic studies. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=107 SRC="FIGDIR/small/739095v1_ufig1.gif" ALT="Figure 1"> View larger version (19K): org.highwire.dtl.DTLVardef@1bbb24eorg.highwire.dtl.DTLVardef@1b74be1org.highwire.dtl.DTLVardef@d6d3ecorg.highwire.dtl.DTLVardef@1f336aa_HPS_FORMAT_FIGEXP M_FIG C_FIG

Redox cofactors are a key part of cellular physiology as they are involved in most metabolic pathways, and their ratios are linked to cellular robustness. However, measuring their levels in cells remains a challenge. Here, we describe a novel method to rapidly measure NAD(H), NADP(H) and nicotinamide mononucleotide (NMN) levels and their oxidized/reduced ratios using an HPLC connected to a fluorescence detector. By extensively characterizing this method and benchmarking it against the classical iodonitrotetrazolium (INT) assay, we show that this method results in accurate and reproducible measurements of NAD+, NADP+ and NMN levels in bacteria. We further demonstrate that this method can be used to determine intracellular NADH and NADPH concentrations and ratios of nicotinamide nucleotide cofactors in engineered Escherichia coli strains, as well as other bacterial species such as Pseudomonas putida.

I.Rapid developments in magic-angle-spinning (MAS) hardware over the past two decades have made possible the acquisition of high-resolution spectra of protons in solids, fuelling studies of small and large molecules alike. Nevertheless, proton resolution, limited by the strong dipole-dipole coupling network, remains a bottleneck even at MAS frequencies exceeding 100 kHz. We present here techniques based on phase-modulated homonuclear decoupling that dramatically improve proton coherence times and resolution compared to 60-95 kHz MAS alone using low average radio-frequency amplitudes (< 100 kHz). A relatively high sensitivity (40- 70%) and a straightforward optimization procedure directly on the sample being studied allows these gains to be realised in large biomolecules, as demonstrated here on a 326-residue cytoskeletal protein in its filamentous state. These techniques enable experiments with improved resolution on biomolecules while simultaneously taking advantage of the higher sensitivity available on probes with relatively large rotor volumes that cannot reach higher MAS frequencies.

We have developed a fluorometric assay for detecting reductase activity in biological samples through 4-methoxy-1-naphthalenemethanol (MONOL-41) formation. The enzyme carbonyl reductase 1 (CBR1) and four members of the aldo-keto reductase (AKR) 1 family (AKR1A1, AKR1B1, AKR1B10, AKR1C3) were evaluated for their ability to reduce 4-methoxy-1-naphthaldehyde (MONAL-41). AKR1B1 and CBR1 followed Michaelis-Menten kinetics, whereas AKR1B10, AKR1A1, and AKR1C3 showed substrate inhibition above 10 {micro}M (70 {micro}M for AKR1C3). Among the tested enzymes, AKR1B10 displayed the highest catalytic efficiency in the absence of substrate inhibition. The MONOL-41 assay was compared with the standard NADPH-based method, showing improved sensitivity, robustness, and lower detection limits (0.77 {micro}g/mL vs. 1.49 {micro}g/mL). These results confirm its suitability for monitoring AKR1B10 activity. The assay was then applied to A549 cell extracts, which express multiple reductases. Activity decreased at substrate concentrations above 10 {micro}M, suggesting a predominant role of AKR1B10. Inhibition studies using tolrestat and high MONAL-41 concentrations indicated a limited contribution of CBR1 ([~]7-8%). Considering both catalytic efficiency and expression levels, AKR1B10 appears to be the main contributor to reductase activity in this model. In A549 living cells, MONAL-41 showed no cytotoxicity up to 50 {micro}M and enabled real-time monitoring due to its membrane permeability. However, oxidation by aldehyde dehydrogenases can generate MONOIC-41, which has similar spectral properties but a lower quantum yield, potentially affecting signal interpretation. Overall, this assay represents a sensitive and cost-effective tool for detecting reductase activity and screening inhibitors.

The primary question in this work is whether a turbidity trace contains more than one resolved kinetic event before any rate or aggregate-mass information is supplied. A blind, three-gate hierarchical Gompertz procedure applied to human interleukin-1 receptor antagonist (IL-1ra) at 53 {degrees}C in phosphate retained one phase at 1 and 2 mg/mL, but selected two phases at 5 and 10 mg/mL. Thus the first resolved multiphase behavior appears at the low protein concentration of 5 mg/mL. Source optical-rate markers were withheld until after selection. Those observed optical rates were then compared with blind-fit phase rates, and the same comparison was expressed on a conditional mass-equivalent scale using the published 5.3-fold Type-I/Type-II turbidity response ratio. A separate 50 {degrees}C citrate series (4, 6, 8, 10, and 14 mg/mL) also selected two phases in every retained trace; its printed Vmax values were used only as post-selection comparators. Finally, two challenging 40 {degrees}C high-concentration traces (180 and 200 mg/mL) were digitized from the instrument-output plot and each retained two phases. All three conditions are analyzed independently. Blind recognition is therefore the central result; the mass-equivalent conversion is a secondary, post-selection interpretation of optical phase rates. The absolute {micro}M/min scale remains conditional on an endpoint aggregate fraction measured elsewhere.

O_LIThe specificity factor(SC/O) of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is a key kinetic parameter quantifying the ratio of carboxylation to oxygenation reactions. Current methods to measure SC/O are expensive, labor-intensive, require specialized expertise, and/or rely on radiolabeled compounds, hindering Rubisco research. C_LIO_LIWe present RubiSpec-MS (Rubisco Specificity by LC-MS/MS), a method to determine the SC/O of purified Rubiscos using liquid chromatography-coupled mass spectrometry (LC-MS/MS) for separation and sensitive detection of non-radioactive reaction products. C_LIO_LIWe benchmark RubiSpec-MS using multiple model Rubisco enzymes. We find that the assay accurately reproduces corresponding literature values for each enzyme and performs similarly in a side-by-side comparison using an established radiometric method. C_LIO_LIRubiSpec-MS provides a faster, more accessible, and highly parallelizable method to measure Rubisco SC/O using equipment common in academic core facilities and industrial laboratories. C_LI

Metabolomics enables the profiling of small-molecule metabolites and thereby captures the biochemical state of a living organism at a given moment and enables to monitor its cellular responses to stimuli. This technique has become a powerful tool in pharmaceutical research, the food industry, and microbial research. Metabolomics aims to obtain an unbiased metabolic profile; however, this is complicated by compound instability, complex and often extensive sample processing, and nonlinear responses in mass spectrometry. Therefore, correcting for metabolite loss and mass spectrometry-related artifacts is essential, typically achieved through relative quantification against an isotopically labelled internal standard for each metabolite of interest. This article describes how to produce 13C-labelled yeast extract and its use as internal standard for metabolomics. More specifically, it provides step-by-step protocols for the fed-batch fermentation, quenching, metabolite extraction, and LC-MS and GC-MS characterization of the internal standard. It also includes a protocol explaining how to use the internal standard for the quantification of metabolites in yeast samples.

Comprehensive detection of steroids, beyond the limited panels typically analyzed in clinical chemistry laboratories, has become increasingly important given their pivotal roles in diverse biological processes. However, steroid quantification poses several analytical challenges, including differences in ionization efficiency and structural similarities across the entire steroid metabolic network. To address these challenges, we developed a targeted ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) assay to analyze 21 steroids using reverse-phase chromatography combined with rapid polarity switching. Mass spectrometry (MS) analysis was performed in scheduled multiple reaction monitoring (sMRM) mode. Depending on the steroid and matrix, the validated lower limits of quantitation (LLOQ) ranged from 12.0 pM to 1216 pM in plasma and 41.1 pM to 384 pM in fecal sample homogenates. In adipose tissue, it was from 0.01 pmol/g to 9 pmol/g. Measured steroid concentrations obtained from the commercial control samples (MassTrak Steroid Serum QC Set 1 and the MassCheck Steroid Panel 1 Serum Control) showed close agreement with the reference values. As a proof of concept, the method was successfully applied to 469 plasma samples in several projects, 15 adipose tissue samples, and 332 fecal samples, demonstrating its applicability to large-scale studies. In conclusion, the method enables sensitive, derivatization-free quantification of an expanded steroid panel in plasma and complex biological matrices, including adipose tissue and fecal samples, representing a significant advancement in comprehensive steroid profiling.

Membrane-bound decarboxylases couple carboxylic acid decarboxylation to the transport of Na+ ions out of prokaryotic cells. The molecular mechanism of decarboxylase action is not yet known, which contrasts with the progress achieved in studying other primary ion pumps. Measuring decarboxylase activity is complicated by slow keto-enol tautomerization of the substrates during the assay. We found that HEPES exhibits anomalously high efficiency as a general acid catalyst for C-H bond formation during the enol-to-ketone conversion of oxaloacetate. Accordingly, the addition of HEPES to the assay medium eliminated the contribution of tautomerization rate to measured decarboxylation rate. Using the dependence of oxaloacetate tautomerization rate and equilibrium on solvent properties and pH, we established that only the keto form of oxaloacetate is converted by Vibrio cholerae oxaloacetate decarboxylase. Steady-state kinetic measurements did not reveal cooperativity in oxaloacetate conversion and Na+ binding. The effects of ionophores (CCCP, valinomycin, and ETH157) on proton transport in pyranine-loaded membrane vesicles prepared from V. cholerae cells indicated that the proton required for the conversion of oxaloacetate to pyruvate is taken up from the cytoplasmic side of the membrane. Furthermore, the effects suggested that {Delta}pH generation is caused by secondary electrophoretic proton transport in exchange for Na+.These findings advance our understanding of the molecular mechanism of the decarboxylation-supported Na+ transport in bacteria.

Background: Mu-opioid receptors (MORs) are expressed throughout the body including in the brain and gastrointestinal (GI) tract. Total-body PET imaging of the brain and GI tract offers a promising approach for cross-sectional in vivo evaluation of the MOR brain-GI axis. However, intestinal motility and bladder filling introduce motion throughout the GI tract over the scan window. Here we establish analysis methodology to account for motion for dynamic imaging of the brain-GI axis, to further characterize peripheral MORs throughout the body and provide a framework for semi-automatic total-body PET modeling. Methods: 4 subjects underwent 90-min dynamic [11C]-carfentanil (cfn) total-body PET acquisitions at baseline, after intravenous naloxone (central antagonist) administration, and after orally administered loperamide (peripheral agonist and P-glycoprotein substrate). Thalamic MOR availability was measured using the Logan reference tissue model. Using CT-based segmentation, the GI tract was subdivided into anatomical segments, in addition to other peripheral organs (e.g., liver, psoas muscle). Frame-by-frame semi-automatic motion correction was performed with three distinct reference frames (11-14 min post-injection, p.i., 35-40 min p.i., and 85-90 min p.i.). The performance of these three were compared to manual correction. Compartment modeling and Logan graphical analysis were performed to estimate relevant kinetic parameters (K1, VT, VTLogan). Results: Across the 4 subjects and regions, kinetic parameter estimates were highly correlated (r>0.7) for K1, VT and VT Logan when comparing semi-automatic (reference frame at 35-40 min p.i.) and manual correction. With semi-automatic motion correction, graphical-based estimation of VTLogan in the gastrointestinal tract was significantly decreased with loperamide relative to baseline (p<0.05). As expected, naloxone decreased brain thalamic MOR availability but loperamide did not. Conclusions: With semi-automatic motion correction and [11C]-cfn total-body PET, pharmacologic perturbations of MOR brain-GI axis can be quantitatively characterized, reducing the burden of image analysis for these studies.

The purification of industrial enzymes typically relies on costly, multi-step chromatographic protocols. To address this, we developed a novel platform termed Coated Bacterial Enzymes (CBEs), which enables one-step purification and immobilization of recombinant proteins fused to the SlpA cell wall binding domain. As a proof of concept, we used a {beta}-galactosidase from Bifidobacterium bifidum of dairy relevance. The chimeric enzyme BbgII-SlpA was expressed in Escherichia coli and captured from crude lysate onto glutaraldehyde-inactivated Bacillus subtilis cells via SlpA domain. Binding was characterized by a dissociation constant (Kd) of 16.2 {micro}M and maximum binding capacity (Bmax) of 144 {micro}mol/g. The resulting CBE biocatalyst exhibited optimal activity at pH 6.0 for ONPG and lactose, with a broader pH profile than the free enzyme. Optimal temperatures were 60 {degrees}C for ONPG and 50 {degrees}C for lactose, and CBE retained >80% activity after 390 min at 45 {degrees}C, compared to 20% for the free enzyme. Catalytic efficiencies (kcat/Km) were 2.62 x106 M-1{middle dot}s-1 for ONPG and 4.40 x102 M-1{middle dot}s-1 for lactose. Moreover, CBE showed improved tolerance to cations such as Ca2+ and Fe2+. These results suggest that the CBE platform offers a cost-effective alternative for producing high-purity, immobilized enzymes for diverse industrial bioprocesses.

Streptavidin-biotin, avidin-biotin interactions are classical models for protein-ligand binding, yet the energetic changes accompanying biotin binding remain poorly resolved. Using fluorescent dyes as energy sensors, we show that biotin binding produces two distinct regimes occurring in parallel as concentration of biotin increases cooperativity and conformational rearrangements, wherein cooperativity is observed via exchange broadening of fluorescence linewidth and conformational rearrangements exclusively observed in emission energy. Where the first biotin binding creates the highest contribution to the emission energy. Further analysis of tetramer-tetramer only interactions revealed extremely long ranged intermolecular interactions extending to hundreds of nm. The intermolecular interactions become negligible only at concentrations of approximately 10 nM for both streptavidin and avidin. Affinity values estimated for these diluted samples were below 1 nM.

Protein oligomerization equilibria are central to many biological processes and are often highly sensitive to environmental conditions such as ionic strength, pH, and ligand binding. Quantitative characterization of these equilibria remains experimentally challenging because stable protein complexes frequently dissociate only at concentrations that are difficult to access with conventional biophysical methods. Fluorescence correlation spectroscopy (FCS) is uniquely suited to this problem, as it provides direct access to diffusion coefficients of fluorescently labeled proteins at nanomolar concentrations. However, the quantitative interpretation of FCS data from oligomeric systems requires a rigorous mathematical framework and careful experimental practice that have not previously been described in sufficient detail to guide implementation. Here, we provide a comprehensive description of the experimental workflow and analytical framework for determining dissociation equilibrium constants by FCS, covering instrument calibration, sample preparation, data quality control, after-pulse correction, and nonlinear least-squares fitting. We discuss common sources of error and provide practical guidance on critical experimental considerations including surface passivation, buffer preparation, equilibration time, and the role of labeling efficiency. Using the homotrimeric sliding clamp PCNA as a model system, we demonstrate the complete workflow under a range of KCl concentrations and show that moderate ionic strength stabilizes the PCNA trimer while very high salt partially destabilizes the complex. The approach is general and applicable to any reversible protein self-association reaction accessible by fluorescence detection at low protein concentrations.

Low-input and single-cell metabolomics remain constrained by the poor retention of polar metabolites in conventional reversed-phase nanoflow LC-MS workflows. Here, we establish nanoflow tributylamine (TBA) ion-pairing LC-MS as a platform for ultra-low-input polar metabolomics and stable isotope tracing. By adapting an analytical-flow TBA ion-pairing method to the nanoflow scale, this workflow extends the sensitivity and inline concentration advantages of nanoflow chromatography to charged metabolites involved in central carbon metabolism. Using mouse liver metabolite extracts, we show that the nanoflow method preserves chromatographic retention and separation of chemically diverse metabolite classes, including adenine nucleotides, nucleotide cofactors, TCA cycle intermediates, acyl-CoAs, and bile acid isomers. Despite loading 20-fold less tissue-equivalent material on column, nanoflow LC-MS produced higher signal intensity than the analytical-flow method for many metabolites. Across representative compounds, the nanoflow workflow reduced the biomass required for detection by approximately 20- to >600-fold, with pronounced gains for low-abundance metabolites such as NADPH and acetyl-CoA. TBA ion-pairing also enabled trap-and-elute nanoflow analysis of retained polar metabolites from single-cell-equivalent inputs. ATP was detected from one cell equivalent using both full-scan and targeted parallel reaction monitoring acquisition, with targeted acquisition further increasing signal over blank. Finally, we applied the workflow to stable isotope tracing in uniformly labeled 13C-glucose-treated cells. 13C-labeled ATP isotopologues were detectable from single-cell-equivalent input, and targeted acquisition improved isotopologue measurement near the detection limit. Together, these results demonstrate that nanoflow TBA ion-pairing LC-MS enables retained, high-sensitivity analysis of polar metabolites from ultra-low inputs and provides a foundation for extending central carbon metabolite analysis and isotope tracing toward single-cell-scale applications.

mRNA technology has emerged as a powerful new class of medicines. Importantly, this RNA-based approach holds promise for treatments beyond vaccines and infectious diseases, including treatments for cancer, metabolic disorders, cardiovascular conditions and autoimmune diseases. The 3'-polyadenylated (poly(A)) tail of mRNA is required for ribosome initiation, translation, and mRNA stability and is considered a critical quality attribute. In this study, novel direct mass spectrometry approaches were used for the analysis of both the DNA template and corresponding mRNA generated via in vitro transcription. Nucleotide resolution of the poly(A/T) sequence of the DNA template and mRNA poly(A) tail was achieved. The results show that the mRNA poly(A) tail length and heterogeneity is impacted by the heterogeneity of the DNA template, the DNA template design and RNA manufacturing conditions, including relative NTP concentrations. These results provide further important mechanistic insight into the poly(A) tail length and heterogeneity of mRNAs synthesised in vitro, including the identification of 3'-end additions of cytidine to mRNA poly(A) tails. The ability to rapidly assess DNA template quality, combined with monitoring mRNA poly(A) tail length and heterogeneity, is important as part of the characterisation of mRNA precision medicines and ensuring consistent quality of mRNA from manufacturing processes.

High dietary fructose consumption is a major contributor to the development of obesity and related cardiometabolic diseases, highlighting the need for accurate assessment of fructose metabolism in humans. Stable isotope tracer approaches, such as 13C6-fructose, require highly sensitive and specific analytical methods to quantify both concentrations and isotopic enrichments. In this study, we developed and validated a robust gas chromatography-triple quadrupole mass spectrometry (GC-QQQ)-based method for the simultaneous measurement of unlabeled and 13C6-fructose in human plasma. The method employs oximation and per-acetate derivatization, and demonstrates high specificity and accuracy. Intra- and inter-assay precision were below 10%, with no detectable carry-over, and a lower limit of quantification (LLOQ) of 0.1 nmol/mL for concentration and 0.02 molar percent excess (MPE%) for enrichment and no interference from glucose. We further compared data acquisition using multiple reaction monitoring (MRM) and selected ion monitoring (SIM). MRM showed superior performance at the low concentrations and enrichment levels characteristic of clinical plasma samples, resulting in improved sensitivity and lower LLOQs compared to SIM. Overall, this validated method provides a sensitive and reliable approach for fructose tracer studies in humans. Its application will facilitate robust investigations into fructose metabolism, and its role in metabolic dysregulation and obesity-related disease.

Obtaining sufficient amounts of pure protein for downstream applications such as native mass spectrometry (nMS) is often challenging, especially when expression yields are low or proteins are unstable. In these cases, the commonly required buffer-exchange step is a major bottleneck, as it often leads to substantial protein loss and compromises biophysical characterization. These challenges are exacerbated in insect or eukaryotic expression systems, where protein yields are typically lower than in bacteria, making protein loss during purification particularly detrimental. Standard lysis and purification buffers contain non-volatile components such as Tris, phosphate, HEPES and sodium chloride, which form adducts during electrospray ionization (ESI) interfering with the signal and therefore must be re-moved prior to nMS. To address protein loss associated with this mandatory buffer-exchange, we evaluated an affinity-purification workflow, in which non-volatile salts are excluded throughout purification and proteins are directly eluted into nMS-compatible ammonium acetate-based buffers. This approach eliminates the need for a separate buffer exchange step and enables rapid nMS analysis immediately after affinity purification. We show that common eluents used in His- and Strep- based affinity purification, such as imidazole, biotin, and desthiobiotin, are well tolerated at relevant concentrations, allowing acquisition of high-quality spectra suitable for determining protein stoichiometry and for monitoring enzymatic or assembly processes. Together, this fast-track affinity workflow increases protein recovery, shortens sample preparation and complements online exchange protocols, which are less suited for monitoring processes. It hence expands the applicability of nMS to proteins and protein complexes that are difficult to obtain in sufficient quantity using conventional purification and buffer exchange strategies.

Members of the transforming growth factor-{beta} (TGF-{beta}) superfamily, including inhibins and activins, are structurally related glycoprotein dimers that regulate reproductive and endocrine signaling. Their high degree of molecular similarity presents challenges for label-free analytical discrimination. To evaluate the ability of Raman spectroscopy to distinguish closely related TGF-{beta} superfamily proteins based on intrinsic vibrational fingerprints. Raman spectra of recombinant human Inhibin -subunit, Inhibin B ({beta}B homodimer), and Activin A ({beta}A--{beta}A) were acquired using confocal Raman microscopy with 532 nm excitation. Spectra were baseline-corrected, area-normalized, and analysed using principal component analysis (PCA). Distinct spectral signatures were observed across the 500--1800 cm-1 region. Differences within the S--S stretching region (500--550 cm-1) were consistent with variations in disulfide-bond environments, with the Inhibin -subunit exhibiting the highest relative intensity in this region. Variations in the amide I band (1600--1700 cm-1) suggested differences in protein secondary structure, while aromatic amino acid vibrations provided additional discriminatory features. PCA revealed clear clustering and separation of all three protein classes based on their Raman fingerprints. Raman spectroscopy enables label-free differentiation of structurally related endocrine glycoproteins and demonstrates potential for the structural characterization and classification of inhibin and activin proteins within the TGF-{beta} superfamily.

Thermostable DNA polymerases are indispensable tools in molecular biology, yet enzymes from the most extreme hyperthermophiles remain largely uncharacterized. Here, we report the biochemical and structural characterization of a family B DNA polymerase from Pyrolobus fumarii A1 (Pyrfu pol), one of the most thermoresistant archaea described to date. The enzyme was efficiently overproduced in E. coli Rosetta 2(DE3)[pLysS] and purified to homogeneity using a two-step protocol that combined heat treatment with immobilized metal affinity chromatography (IMAC). Bioinformatic analysis confirmed the canonical family B architecture, while AlphaFold-based structural modeling and comparative analysis with mesophilic RB69 DNA polymerase revealed a well-conserved structural core alongside thermoadaptive features. Radiolabel incorporation assays demonstrated enzymatic activity over a broad ionic strength range and an absolute requirement for Mg ions. PCR-based optimization confirmed these findings and revealed broad pH tolerance (6.5-11.0). Notably, Tris inhibited radiolabel-based assays (pH 7.0) yet proved essential for efficient PCR amplification (pH 8.5), suggesting a context-dependent role of buffer composition in polymerase activity. Processivity assays confirmed amplification of DNA fragments up to approximately 8,000 bp. Replication fidelity, assessed by the lacZ-based assay, showed a 2.9-fold improvement over Taq polymerase. Urea-nanoDSF yielded an exceptional melting temperature of 105.9 {+/-} 0.08 {degrees}C. Pyrfu pol also demonstrated tolerance to common PCR inhibitors, highlighting its potential utility in molecular biology applications.