Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.12.7.2 (hydrogenase)
3,522 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Methanol: 5-hydroxybenzimidazolylcobamide methyltransferase (MT1) from Methanosarcina barkeri, which is one of the enzymes responsible for the transmethylation from methanol to coenzyme M, was found to be activated in the presence of hydrogenase and ferredoxin. This activation was shown to involve a reduction of the bound corrinoid to the Co (I) level, and was demonstrated by spectrophotometry and chemical conversion of reduced MT1 to its methylated form. The reducing system of hydrogenase and ferredoxin was able to reduce dithiols, like dithiodiethanesulfonate and cystine to their monomers, in the presence of a corrinoid, which acts as an electron carrier. The ferredoxin was purified 133-fold and was tentatively identified on the basis of spectral properties and iron content of 3.8-4.0 atoms iron per molecule ferredoxin (12,000 daltons).
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PMID:Reductive activation of methanol: 5-hydroxybenzimidazolylcobamide methyltransferase of Methanosarcina barkeri. 636 42

It has been demonstrated that enzymes from Clostridium thermoaceticum catalyze the following reaction in which Fd is ferredoxin and CH3THF is methyltetrahydrofolate. (for formula see text). The system involves hydrogenase, CO dehydrogenase, a methyltransferase, a corrinoid enzyme and other unknown components. Hydrogenase catalyzes the reduction of ferredoxin by H2; CO dehydrogenase then uses the reduced ferredoxin to reduce CO2 to a one-carbon intermediate that combines with CoASH and with a methyl group originating from CH3THF to form acetyl-CoA. It is proposed that these reactions are part of the mechanism which enables certain acetogenic autotrophic bacteria to grow on CO2 and H2.
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PMID:The synthesis of acetyl-CoA by Clostridium thermoaceticum from carbon dioxide, hydrogen, coenzyme A and methyltetrahydrofolate. 642 23

Methanol:5-hydroxybenzimidazolylcobamide methyltransferase from Methanosarcina barkeri has been purified to approximately 90% homogeneity by ion-exchange chromatography on DEAE-cellulose and QAE-A50 Sephadex columns. The molecular weight, estimated by gel electrophoresis, was found to be 122,000, and the enzyme contained two different subunits with molecular weights of 34,000 and 53,000, which indicates an alpha 2 beta structure. The enzyme contains three or four molecules of 5-hydroxybenzimidazolylcobamide, which could be removed by treatment of the enzyme with 2-mercaptoethanol or sodium dodecyl sulfate. In both cases the enzyme dissociated into its subunits. For stability, the enzyme required the presence of divalent cations such as Mg2+, Mn2+, Sr2+, Ca2+, or Ba2+. ATP, GTP, or CTP was needed in a reductive activation process of the enzyme. This activation was brought about by a mixture of H2, ferredoxin, and hydrogenase, but also by CO, which is thought to reduce the corrinoid chemically. The CO dehydrogenase-like activity of the methyltransferase is discussed.
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PMID:Purification and properties of methanol:5-hydroxybenzimidazolylcobamide methyltransferase from Methanosarcina barkeri. 643 59

The genes encoding the two isoenzymes of methyl coenzyme M reductase (MRI and MRII) in Methanobacterium thermoautotrophicum delta H have been cloned and sequenced. The MRI-encoding mcr operon (mcrBDCGA) has been located immediately upstream from the mtr operon (mtrEDCBA) that encodes N5-methyltetrahydromethanopterin:coenzyme M methyltransferase, the enzyme that catalyzes the step preceding the MR-catalyzed reaction in methanogenesis. The MRII-encoding mrt operon (mrtBDGA) has been located between the operon that encodes the methyl viologen-reducing hydrogenase and an open reading frame (designated pyrC) predicted to encode dihydroorotase. Surprisingly, the mrt operon has been found to contain only four genes (mrtBDGA), lacking the equivalent of the mcrC gene that is present in all mcr operons. A protocol that isolates transcripts intact from M. thermoautotrophicum delta H cells has been developed and used, with primer extension and Northern (RNA) blot procedures, to identify the sites of transcription initiation upstream of the mcr, mrt, and mtr operons and to determine the relative numbers of these transcripts in cells at different growth stages. Transcription of the mrt operon was found to occur only at early times in batch cultures and was then replaced by transcription of the mcr operon. Transcripts of the mtr operon were detectable at all times; however, at early times, all mtr transcripts were initiated at the mtr promoter, whereas at later times, during mcr transcription, approximately 3% of mcr transcripts were extended to generate mcr plus mtr transcripts that constituted approximately 20% of all mtr transcripts present.
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PMID:Growth phase-dependent transcription of the genes that encode the two methyl coenzyme M reductase isoenzymes and N5-methyltetrahydromethanopterin:coenzyme M methyltransferase in Methanobacterium thermoautotrophicum delta H. 792 10

Methanol:5-hydroxybenzimidazolylcobamide methyltransferase (MT1) is the first of two enzymes required for transfer of the methyl group of methanol to 2-mercaptoethanesulfonic acid in Methanosarcina barkeri. MT1 binds the methyl group of methanol to its corrinoid prosthetic group only when the central cobalt atom of the corrinoid is present in the highly reduced Co(I) state. However, upon manipulation of MT1 and even during catalysis, the enzyme becomes inactivated as the result of Co(I) oxidation. Reactivation requires H2, hydrogenase, and ATP. Ferredoxin stimulated the apparent reaction rate of methyl group transfer. Here we report that one more protein fraction was found essential for the overall reaction and, more specifically, for formation of the methylated MT1 intermediate. The more of the protein that was present, the shorter the delay of the start of methyl group transfer. The maximum velocity of methyl transfer was not substantially affected by these varying amounts of protein. This demonstrated that the protein was involved in the activation of MT1. Therefore, it was called methyltransferase activation protein.
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PMID:Involvement of an activation protein in the methanol:2-mercaptoethanesulfonic acid methyltransferase reaction in Methanosarcina barkeri. 844 90

In Methanosarcina barkeri the transfer of the methyl group from methanol to 2-mercaptoethanesulfonic acid is catalyzed by the concerted action of two methyltransferases. The first one is the corrinoid-containing methanol:5-hydroxybenzimidazolylcobamide methyltransferase (MT1), which binds the methyl group of methanol to its corrinoid prosthetic group. MT1 is only catalytically active when the cobalt atom of the corrinoid is present in the highly reduced Co(I) state. In the course of its purification and even during catalysis, MT1 becomes oxidatively inactivated. The enzyme, however, may be reductively reactivated by a suitable reducing system (hydrogen and hydrogenase), ATP, and an enzyme called methyltransferase activation protein (MAP). In order to elucidate its role in the reactivation process, MAP was purified to apparent homogeneity. The protein had an Mr = 60,000. Preincubation of the enzymic components involved with 8-azido-ATP or with ATP demonstrated MAP to be the primary site of action of ATP. In agreement herewith, the protein was autophosphorylated by [gamma-32P]ATP in a 1:1 stoichiometry. Phosphorylated MAP substituted for ATP in the activation of MT1, and the addition of increasing amounts of MAP phosphate resulted in a corresponding increase of active MT1. However, in the presence of limiting amounts of MAP, maximal activation of MT1 could be achieved during a lag phase provided ATP was present, indicating that MAP acts as a catalyst. This paper is the first to report on the presence, isolation, and function of a phosphorylated protein in a methanogenic archaeon.
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PMID:Purification and properties of an enzyme involved in the ATP-dependent activation of the methanol:2-mercaptoethanesulfonic acid methyltransferase reaction in Methanosarcina barkeri. 879 94

Methanol:5-hydroxybenzimidazolylcobamide methyltransferase (MT1) is the first of two enzymes involved in the transmethylation reaction from methanol to 2-mercaptoethanesulfonic acid in Methanosarcina barkeri. MT1 only binds the methyl group of methanol when the cobalt atom of its corrinoid prosthetic groups is present in the highly reduced Co(I) state. Formation of this redox state requires H2, hydrogenase, methyltransferase activation protein, and ATP. Optical and electron paramagnetic resonance spectroscopy studies were employed to determine the oxidation states and coordinating ligands of the corrinoids of MT1 during the activation process. Purified MT1 contained 1.7 corrinoids per enzyme with cobalt in the fully oxidized Co(III) state. Water and N-3 of the 5-hydroxybenzimidazolyl base served as the upper and lower ligands, respectively. Reduction to the Co(II) level was accomplished by H2 and hydrogenase. The cob(II)amide of MT1 had the base coordinated at this stage. Subsequent addition of methyltransferase activation protein and ATP resulted in the formation of base-uncoordinated Co(II) MT1. The activation mechanism is discussed within the context of a proposed model and compared to those described for other corrinoid-containing methyl group transferring proteins.
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PMID:Activation mechanism of methanol:5-hydroxybenzimidazolylcobamide methyltransferase from Methanosarcina barkeri. 879 95

The ether-cleaving O-demethylase isolated from syringate-grown cells of Acetobacterium dehalogenans (formerly named strain MC) consists of four proteins, components A, B, C and D. The enzyme system converts only phenyl methyl ethers with a hydroxyl group in the ortho position to the methoxyl moiety. The presence of a carboxyl group in the aromatic compound was not required for O-demethylase reaction. Component B mediated the conversion of vanillate to 3,4-dihydroxybenzoate in the presence of the Ti(III)-reduced corrinoid-containing component A. After addition of component D and tetrahydrofolate, methyl tetrahydrofolate was formed from vanillate in stoichiometric amounts. Titanium(III) citrate as a reductant could be replaced by H2, methyl viologen or ferredoxin, partially purified hydrogenase, purified component C obtained from A. dehalogenans, and ATP. From these findings, it was deduced that component B serves as vanillate:corrinoid protein methyltransferase (methyltransferase I) mediating the methyl transfer from vanillate to the reduced corrinoid protein component A. Component D functions as methylcorrinoid protein:tetrahydrofolate transferase (methyltransferase II). The role of component C is probably that of an activating protein reversing accidental oxidation of the protein-bound cob(I)alamin to cob(II)alamin in the presence of ATP and reducing equivalents supplied by the enzymatic oxidation of hydrogen.
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PMID:O-demethylase from Acetobacterium dehalogenans--substrate specificity and function of the participating proteins. 965 69

Dimethylamine/5-hydroxybenzimidazolylcobamide methyltransferase (DMA-MT) from Methanosarcina barkeri Fusaro catalyzes (Vmax = 4700 nmol x min(-1) x mg(-1) protein; k(cat) = 7.8 s(-1)) the transfer of a methyl group from dimethylamine (apparent Km = 0.45 mM) to its corrinoid prosthetic group to yield monomethylamine (MMA) and the methylated enzyme. The product, MMA, is a competitive inhibitor of the reaction (apparent Ki = 5.5 mM). The methyl group bound to the corrinoid prosthetic group of DMA-MT is subsequently transferred to coenzyme M in a reaction mediated by methylcobalamin/coenzyme M methyltransferase isoenzyme II [MT2(II)], which binds with high affinity to DMA-MT (apparent Km = 0.22 microM). As isolated, DMA-MT is inactive, but it can enzymically be reactivated by methyltransferase activating protein (MAP), ATP, and hydrogenase. Apart from the established role in corrinoid activation, ATP was found to act as a powerful allosteric effector on the methyltransferase reaction. The results of kinetic studies, supported by the resolution of as-yet partially purified auxiliary protein fractions, demonstrate that DMA-MT, MT2(II), MAP, and hydrogenase are the only enzymic components involved in the dimethylamine/coenzyme M methyltransfer in M. barkeri Fusaro.
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PMID:Activation and reaction kinetics of the dimethylamine/coenzyme M methyltransfer in Methanosarcina barkeri strain Fusaro. 987 28

Environmental chemicals with estrogenic activities have been suggested to be able to interact with the endocrine system. Endogenous estrogen is synthesized in the ovarian theca cells of premenopausal women or in the stromal adipose cells of the breast of postmenopausal women and minor quantities in peripheral tissue. These cells, as well as breast tissue, express all the necessary enzymes for this synthesis, CYP17, CYP11a, CYP19, 17-beta-hydroxysteroid hydrogenase, steroid sulfatase as well as enzymes further hydroxylating estradiol, such as CYP1A1, CYP3A4, CYP1B1, catechol-o-methyltransferase (COMT). Polymorphisms in these enzymes may have a possible role in the link between environmental estrogens and hormone-like substances and the interindividual risk of breast cancer.
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PMID:Genetic susceptibility and environmental estrogen-like compounds. 1153 51


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