Inducible and repressible acetylornithine delta-transaminase in Escherichia coli: different proteins

Two acetylornithine δ-transaminases which have different physical and kinetic properties have been isolated from a mutant of E. coli W. Sephadex gel filtration has shown the molecular weight of one transaminase to be approximately 119,000; the second transaminase has a molecular weight of about 61,000. The two transaminases can be separated by ammonium sulfate fractionation. The K_m values of the smaller and larger molecular-weight species for N^α-acetylornithine are 3.1 mm and 1.3 mm, respectively. The K_m for α-ketoglutarate is 1.1 mm for both enzymes. The presence of arginine in the growth medium represses the synthesis of the 119,000 molecular-weight transaminase and induces the synthesis of the 61,000 molecular-weight species.