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Aspartate-β-semialdehyde dehydrogenase, from an Escherichia coli mutant derepressed for the biosynthesis of l-lysine, has been purified to homogeneity. Its isoelectric point is pH 4.3. This enzyme has a molecular weight of 77000 and is composed of two identical or highly similar subunits of molecular weight 38000 ± 2000.

Their N-terminal amino-acid sequence is Met-Lys-Asx-Val-Gly-. Three cysteine residues per subunit were detected: two are reactive in the native enzyme and one is partially protected by the substrate. Formation of an acyl-enzyme intermediate was also detected. Correlation of the 1H nuclear magnetic resonance spectrum of [4-2H]NADPH produced from [4-2H]NADP+ indicated that aspartate β-semialdehyde dehydrogenase transfers the pro-S hydrogen from NADPH (class B dehydrogenase). A short comparison with the corresponding yeast enzyme is given.