AMP metabolism by the marine bacterium Vibrio (Beneckea) natriegens: purification and properties of adenylate kinase

Adenylate kinase (EC 2.7.4.3) has been purified 484-fold from extracts of Vibrio natriegens to a specific activity of 1350 μmol ADP formed∙min−1∙mg protein−1. The preparation was 97% pure as judged by gel electrophoresis and exhibited molecular weight values of 29 000 by gel filtration and 32 000 by SDS–gel electrophoresis. The isoelectric point was at pH 4.7. Only ATP (Km 0.067 mM), ADP (Km 0.45 mM), and AMP (Km 0.12 mM) exhibited high activity as substrates, though dATP or dAMP could serve as cosubstrates with AMP or ATP, respectively, at reduced rates. The equilibrium constant in the direction of ATP formation was 1.09, and the pH optimum in both directions was broad, from pH 7.2 to pH 7.6. Enzyme activity was sensitive to the thiolalkylating agents iodacetamide and p-chloromercuriphenyl sulfonate.

AMP metabolism in the marine bacterium Beneckea natriegens

The catabolism of AMP by preparations from Beneckea natriegens has been reexamined. In the absence of ATP, cell-free extracts catabolized AMP via adenosine to inosine. When ATP was present, adenylate kinase converted AMP to ADP, lowering the rate of AMP catabolism. Particle-free supernatants (225 000 × g) metabolized AMP alone slowly, but adenylate kinase was active when ATP was added. Washed particulate fractions contained AMP nucleotidase activity which converted AMP to adenosine; in the presence of ATP, adenosine formation was reduced by residual adenylate kinase associated with the particulate fraction. IMP was not detected as a metabolite in these experiments.