RESUMO
The enzyme adenylate kinase (ATP:AMP phosphotransferase) was purified as described previously [Biochim. Biophys. Acta 869: 350 (1986)] with an additional step involving affinity chromatography on Cibacron Blue. The molecular weight of the final enzyme preparation was estimated to be 22,500 on polyacrylamide-gel electrophoresis under denaturing conditions. The preliminary amino acid analysis indicated the presence of two histidine residues. Photooxidation in the presence of methylene blue caused complete inactivation of the enzyme, but the loss of activity could be prevented by the addition of ATP, AMP or adenosine-(5')-pentaphospho-(5')-adenosine, indicating that at least one histidine residue is involved at the active site. A circular dichroic study indicated that the enzyme consists of 24% alpha-helix, 30% beta-structure, and 46% random coil. The bacterial cells induced with antimycin A and light (particularly with the former) appeared to have somewhat increased adenylate kinase activity, although the Km and Vmax values were unchanged.