Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.6.1.19 (GABA transaminase)
 808 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

4-Aminobutyrate aminotransferase is inactivated by preincubation with iodosobenzoate at pH 7. The reaction of 2 SH residues/dimer resulted in formation of an oligomeric species of Mr = 100,000 detectable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The subunits cross-linked via a disulfide bond are dissociated by addition of 2-mercaptoethanol which also restores full catalytic activity (Choi, S. Y., and Churchich, J.E. (1985) J. Biol. Chem. 260, 993-997). The substrate 2-oxoglutarate prevents inactivation of the enzyme by iodosobenzoate and the subsequent formation of one disulfide bond, whereas 4-aminobutyrate has no effect on the reactivity of SH groups with iodosobenzoate. Modified 4-aminobutyrate aminotransferase (containing 1 disulfide bond) catalyzes a half-transamination reaction; but it is unable to react with 2-oxoglutarate to generate the aldimine form of the enzyme. The spectroscopic properties (fluorescence yield and polarization of fluorescence) of PMP bound to the modified enzyme are different from those of pyridoxamine phosphate (PMP) bound to the native enzyme. The polarization of fluorescence values of PMP bound to the cross-linked enzyme, excited over the spectral range 310-370 nm, are greater (25%) than those of the cofactor of the native enzyme. An increase in the polarization values implies that the motion of PMP is restricted when the subunits are cross-linked via a disulfide bond.
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PMID:The reversible oxidation of vicinal SH groups in 4-aminobutyrate aminotransferase. Probes of conformational changes. 365 61

4-Aminobutyrate aminotransferase is inactivated by preincubation with N-(1-pyrene)maleimide (mixing molar ratio 10:1) at pH 7. The reaction with N-(1-pyrene)maleimide was monitored by fluorescence spectroscopy and the degree of labeling of the enzyme determined by absorption spectroscopy. The blocking of 2 cysteinyl residues/enzyme dimer is needed for inactivation of the aminotransferase. The time course of the reaction is significantly affected by the substrate alpha-ketoglutarate, which afforded complete protection against the loss of catalytic activity. Trypsin digestion of pyrene-labeled aminotransferase, followed by gel filtration and "fingerprint" analysis, revealed the presence of only one peptide tagged with the fluorescent probe. The reaction of approximately 1.9 SH residues/dimer with iodosobenzoate resulted in enzyme inactivation together with a formation of an oligomeric species of Mr = 100,000 detectable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The cross-linked subunits are dissociated by addition of 2-mercaptoethanol which also restores full catalytic activity. Altogether, these observations are consistent with the concept that inactivation of 4-aminobutyrate aminotransferase by iodosobenzoate proceeds through disulfide bond formation between vicinal cysteinyl residues of the protein. It is postulated that the critical sulfhydryl groups of the enzyme are situated on opposite sides of the dimeric structure at the subunit interfaces.
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PMID:4-Aminobutyrate aminotransferase reaction of sulfhydryl residues connected with catalytic activity. 396 74

Previously it was found that a conformationally rigid analogue (2) of the epilepsy drug vigabatrin (1) did not inactivate gamma-aminobutyric acid aminotransferase (GABA-AT). A cyclic compound with an exocyclic double bond (6) was synthesized and was found to inactivate GABA-AT, but only in the absence of 2-mercaptoethanol. The corresponding difluoro-substituted analogue (14) was synthesized and was shown to be a very potent time-dependent inhibitor, even in the presence of 2-mercaptoethanol.
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PMID:Design, synthesis, and biological activity of a difluoro-substituted, conformationally rigid vigabatrin analogue as a potent gamma-aminobutyric acid aminotransferase inhibitor. 1464 May 37