Specificity and some other properties of liver serine sulphhydrase: evidence for its identity with cystathionine -synthase.

摘要: Abstract 1. The catalytic properties of extensively purified preparations chicken liver serine sulphhydrase (I; EC 4.2.1.22) and rat cystathionine β-synthase (II; 4.2.1.13) have been investigated in parallel. These two pyridoxal -P- dependent enzymes catalysed similar sets reactions involving replacement polar groups l -serine, β-substituted analogues serine, -cysteine or its S- alkyl derivatives, on incubation with a variety mercapto compounds, resulting production corresponding thioethers. Both failed to catalyse α,β-elimination reactions. 2. Measurement the respective K m values showed that (II) exhibited higher affinities for substrate cosubstrate reaction synthesis from -serine homocysteine, whereas (I) had slightly (and potency) displacement H2S cysteine presence β-mercaptoethanol. 3. Inhibitor sensitivities ( I 50 values) were likewise closely similar: II, like enzyme I, was strongly inhibited by hydroxylamine aminooxyacetate (10−4 M); both practically insensitive dl -cycloserine d - -penicillamine-potent inhibitors aminotransferases α,β-eliminating (e.g. γ-cystathionase). 4. Fractionation crude extracts containing under study, electrofocusing, subfractionation Biogel P-200 columns revealed, each case, only one protein peak coincident activity maxima (a) + (b) release compounds. isoelectric points, determined ampholine electrophoresis, different (pH 6.0) II 5.5). 5. body evidence indicates existence, homoiothermic animals, single catalusing formation (also analogous β-thioethers free cysteine) either way β-replacement reations. observed differences some values, relative velocities, molecular weight etc.) teh obtained form biological sources are attributable genetically determined, species-specific variation enzyme. Centrain β-replacing thiol-lyases organisms other classes (e.g microorganisms plants, see ref. 28–30) probably belong same group, family, plurifunstional enzymes.