title: Succinic semialdehyde dehydrogenases of Escherichia coli: their role in the degradation of p-hydroxyphenylacetate and gamma-aminobutyrate.
abstract: Two physically and genetically distinct forms of succinic-semialdehyde dehydrogenase have been identified in Escherichia coli B. The two enzymes could be separated by filtration on Sephadex G-150 and their apparent molecular weights were 200 000 and 97 000. The larger enzyme, which is specific for NADP, is induced by growth on gamma-aminobutyrate. Its induction is highly coordinated with that of gamma-aminobutyrate:2-oxoglutarate transaminase, the enzyme which initiates degradation of gamma-aminobutyrate. The smaller enzyme, which is induced by growth on p-hydroxyphenylacetate, has been purified to 98% homogeneity by affinity chromatography in conjunction with conventional methods. Under standard assay conditions this enzyme acts preferentially with NAD but reduces NADP at 15% of the rate observed for NAD, primarily because of a difference in Km. Apparent Km values for succinic semialdehyde and NAD are 13.3 +/- 1.3 microM and 33.7 +/- 1.4 microM, respectively. The subunit molecular weight was estimated to be 55 000, indicating that the native enzyme is dimeric. The NAD-dependent succinic-semialdehyde dehydrogenase is also induced by exposure of cells to exogenous succinic semialdehyde, a treatment which has no effect on the amount of other enzymes of p-hydroxyphenylacetate or gamma-aminobutyrate metabolism. Apparently the gene for this enzyme functions independently from the genes encoding the other enzymes of p-hydroxyphenyl-acetate degradation. As a consequence of its induction mechanism, this NAD-dependent dehydrogenase is also present in extracts of E. coli B grown with gamma-aminobutyrate as sole nitrogen source, in addition to the NADP-specific enzyme involved in gamma-aminobutyrate metabolism. Presumably the NAD-dependent enzyme is gratuitously induced by succinic semialdehyde formed by transamination of gamma-aminobutyrate.
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000302:isolation & purification / Q000378:metabolism*; D004790:Enzyme Induction / Q000187:drug effects; D004926:Escherichia coli / Q000378:metabolism*; D009243:NAD / Q000494:pharmacology; D009249:NADP / Q000494:pharmacology; D010648:Phenylacetates / Q000378:metabolism*; D050604:Succinate-Semialdehyde Dehydrogenase (NADP+); D005680:gamma-Aminobutyric Acid / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D010648:Phenylacetates; D009243:NAD; C026246:4-hydroxyphenylacetate; D009249:NADP; D005680:gamma-Aminobutyric Acid; D000445:Aldehyde Oxidoreductases; D050604:Succinate-Semialdehyde Dehydrogenase (NADP+); C009338:succinic semialdehyde