Role of 4 aminobutyrate aminotransferase in the arginine metabolism of Pseudomonas aeruginosa

Abstract

4 Aminobutyrate aminotransferase (GABAT) from P. aeruginosa was purified 64 fold to apparent electrophoretic homogeneity from cells grown with 4 aminobutyrate as the only source of carbon and nitrogen. Purified GABAT catalyzed the transamination of 4 aminobutyrate, N2 acetyl L ornithine, L ornithine, putrescine, L lysine, and cadaverine with 2 oxoglutarate (listed in order of decreasing activity). The enzyme is induced in cells grown on 4 guanidinobutyrate, 4 aminobutyrate, or putrescine as the only carbon and nitrogen source. Cells grown on arginine or on glutamate contained low levels of the enzyme. The regulation of the synthesis of GABAT as well as the properties of a mutant with an inactive N2 acetyl L ornithine 5 aminotransferase suggest that GABAT functions in the biosynthesis of arginine by converting N2 acetyl L glutamate 5 semialdehyde to N2 acetyl L ornithine as well as in catabolic reactions during growth on putrescine or 4 guanidinobutyrate but not during growth on arginine.