Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.4 (trypsin)
 42,187 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The sensitivity of the membrane-bound hydrogenase of Bradyrhizobium japonicum to inactivation by proteases and membrane-impermeant protein modification reagents was compared under hydrogen versus oxygen. In membrane vesicles, the half-life of enzyme inactivation by trypsin of the H2-reduced enzyme was approximately 10 min, whereas O2-oxidized enzyme was much less sensitive to trypsin inactivation (half-life of over 90 min). Diazobenzene sulfonate (DABS) affected the enzyme activity in a manner similar to proteases. With DABS, the enzyme had a half-life of 2-3 min under H2 versus over 30 min under O2. Experiments in which the gas phase (containing either H2 or O2) available to the membranes was changed prior to the protease or chemical modification treatments indicated that it is the redox state of the enzyme at the time of the treatment which determines the sensitivity of the enzyme to inactivation. The redox-dependent differences in the behavior of the membrane-bound enzyme were attributed to changes in the accessibility of the small (33 kDa) subunit. The kinetics of enzyme inactivation by trypsin, under H2, correlated very well with the degradation of the intact 33-kDa subunit, whereas the large subunit (65 kDa) was rather resistant to proteolytic degradation. DABS treatment was found to decrease the reactivity of the small subunit to its antibody concomitant with enzyme inactivation under H2, but without such an effect on the O2-oxidized enzyme. In contrast to the results with the membrane-bound enzyme, purified dehydrogenase was found to be equally susceptible to inactivation by proteolysis or chemical modification irrespective of whether the treatments were performed under H2 or O2. These results indicate that, in the membrane, hydrogenase undergoes a redox-linked conformational change, whereby the small subunit of the enzyme becomes more accessible to external reagents when the enzyme is in its reduced form.
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PMID:Conformational changes in the membrane-bound hydrogenase of Bradyrhizobium japonicum. Evidence that the redox state of the enzyme affects its accessibility to protease and membrane-impermeant reagents. 305 19

An active tryptic fragment of membrane-bound hydrogenase isoenzyme 2 from anaerobically grown Escherichia coli has been purified. The soluble enzyme derivative was released from the membrane fraction by trypsin cleavage. The purification procedure involved ion-exchange, hydroxyapatite and gel permeation chromatography. The enzyme derivative was purified 100-fold from the membrane fraction and the specific activity of the final preparation was 320 mumol benzyl viologen reduced min-1 mg protein-1 (H2:benzyl viologen oxidoreductase). The native enzyme derivative had an Mr of 180,000 and was composed of equimolar amounts of polypeptides of Mr 61,000 and 30,000. It possessed 12.5 mol Fe, 12.8 mol acid-labile S2- and 3.1 mol Ni/180,000 g enzyme. Antibodies were raised to the purified preparation which cross-reacted with hydrogenase isoenzyme 2 but not with isoenzyme 1 in detergent-dispersed preparations. Western immunoblot analysis revealed that isoenzyme 2 which had not been exposed to trypsin contained cross-reacting polypeptides of Mr 61,000 and 35,000. Trypsin treatment of the membrane-bound enzyme to form the soluble derivative of isoenzyme 2, therefore, cleaves a polypeptide of Mr 35,000 to produce the 30,000-Mr fragment. Trypsin treatment of the detergent-dispersed isoenzyme 2 produces the same fragmentation of the enzyme. Neither of the subunits of the enzyme revealed any immunological identity with those of hydrogenase isoenzyme 1.
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PMID:Isolation and characterisation of a soluble active fragment of hydrogenase isoenzyme 2 from the membranes of anaerobically grown Escherichia coli. 351 90

Two membrane-bound hydrogenase isoenzymes present in Escherichia coli during anaerobic growth have been resolved. The isoenzymes are immunologically and electrophoretically distinct. The physically more abundant isoenzyme (hydrogenase 1) contains a subunit of Mr 64,000 and is not released from the membrane by exposure to either trypsin or pancreatin. The second isoenzyme (hydrogenase 2) apparently contributes the greater part of the membrane-bound hydrogen:benzyl viologen oxidoreductase activity and exists in two electrophoretic forms revealed by nondenaturing polyacrylamide gel analysis. This isoenzyme is irreversibly inactivated at alkaline pH and gives rise to an active, soluble derivative when the membrane-bound enzyme is exposed to either trypsin or pancreatin. Both hydrogenase isoenzymes contain nickel.
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PMID:Nickel-containing hydrogenase isoenzymes from anaerobically grown Escherichia coli K-12. 389 25

Desulfotomaculum reducens strain MI-1 is a Gram-positive, sulfate-reducing bacterium also capable of reducing Fe(III). Metal reduction in Gram-positive bacteria is poorly understood. Here, we investigated Fe(III) reduction with lactate, a non-fermentable substrate, as the electron donor. Lactate consumption is concomitant to Fe(III) reduction, but does not support significant growth, suggesting that little energy can be conserved from this process and that it may occur fortuitously. D. reducens can reduce both soluble [Fe(III)-citrate] and insoluble (hydrous ferric oxide, HFO) Fe(III). Because physically inaccessible HFO was not reduced, we concluded that reduction requires direct contact under these experimental conditions. This implies the presence of a surface exposed reductase capable of transferring electrons from the cell to the extracellular electron acceptor. With the goal of characterizing the role of surface proteins in D. reducens and of identifying candidate Fe(III) reductases, we carried out an investigation of the surface proteome (surfaceome) of D. reducens. Cell surface exposed proteins were extracted by trypsin cell shaving or by lysozyme treatment, and analyzed by liquid chromatography-tandem mass spectrometry. This investigation revealed that the surfaceome fulfills many functions, including solute transport, protein export, maturation and hydrolysis, peptidoglycan synthesis and modification, and chemotaxis. Furthermore, a few redox-active proteins were identified. Among these, three are putatively involved in Fe(III) reduction, i.e., a membrane-bound hydrogenase 4Fe-4S cluster subunit (Dred_0462), a heterodisulfide reductase subunit A (Dred_0143) and a protein annotated as alkyl hydroperoxide reductase but likely functioning as a thiol-disulfide oxidoreductase (Dred_1533).
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PMID:Characterization of the surfaceome of the metal-reducing bacterium Desulfotomaculum reducens. 2519 10