Aspartate‐β‐Semialdehyde Dehydrogenase from Escherichia coli

Aspartate-beta-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 nucleár magnetic resonance spectrum of [4-2H]NADPH produced from [4-2H]NADP+ indicated that aspartate beta-semialdehyde dehydrogenase transfers the pro-S hydrogen from NADPH (class B dehydrogenase). A short comparison with the corresponding yeast enzyme is given.