Acetylornithine 3-transaminase

In an argR derivative of strain K12, but not in a corresponding argR derivative, magnesium ions, at the relatively high concentration of 0.4 M, were found to reduce the activity of acetylornithine -transaminase [72]. This repression-dependent reduction in activity reflects a reversible alteration of the enzyme, as illustrated in Fig. 5 (Leisinger et al. [67]). In view of the requirement for repressive conditions, it was... 

Acetylornithine S-transaminase a-A/-Acetyl-L-omithine 2-oxogluta-rate aminotransferase (EC 2.6.1.11)... 

A -acetylglutamic y-semialdehyde dehydrogenase [4, 7], acetylornithine 5-transaminase [1, 8, 9], acetylornithinase [1, 10, 11], ornithine trans-carbamylase [12], and argininosuccinase [13] have been partially purified and characterized. A -Acetylglutamate synthetase activity has been exhibited in extracts [14], and this enzyme, which catalyzes the first step of the pathway, has been shown in cell suspension experiments to be subject to feedback inhibition by arginine [15],... 

Fig. 6. A Formation of acetylornithine S-transaminase in strain 39A-23R3 of Escherichia coli under physiological derepression (growth on V -acetyl-L-omithine, 0.05 mg/ml), in the absence (open circles) or presence (solid circles) of streptomycin sulfate (6/x.g/ml). B Formation of acetylornithine S-transaminase in the same strain under repression (growth on L-arginine hydrochloride, 0.2 mg/ml), in the absence (open triangles) or presence (solid triangles) of streptomycin sulfate (6 /ng/ml). Cf. Vogel and Vogel [102].

Similar experiments were carried out with tetracycline instead of streptomycin, and very similar results were obtained [103]. In addition to the argR strain, an argR strain was examined, as well as another mutant strain (grgR ) with diminished repressibility and diminished derepressibility [103]. For these strains, too, streptomycin and tetracycline behaved alike. Data obtained with tetracycline are listed in Table II. With respect to acetylornithine 5-transaminase and arginino-succinase, for the argR strain, the differential rates are seen to be... 

Strain Growth supplement Inhibitor Acetylornithine 8-transaminase Argininosuccinase... 

Three relevant enz3une activities have been demonstrated in E. coli extracts. These are an acetylase which forms JV-acetylglutamate from glutamic acid and acetyl CoA 129), a transaminase which forms N -acetylornithine 116), and acetylomithinase which hydrolyzes the N -acetylomithine to ornithine 116). It is highly significant that the last named enz3une was absent in extracts of a mutant blocked between iV -acetylomithine and ornithine 116). 

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