Identification and purification of an adenylate kinase-associated protein that influences the thermolability of adenylate kinase from a temperature-sensitive adk mutant of Escherichia coli.

Adenylate kinase prepared from a temperature-sensitive adk mutant of Escherichia coli was thermolabile at 40 degrees C while the wild type enzyme was stable. The degree of thermolability of the mutant enzyme was concentration-dependent in that a much greater thermolability was observed in the concentrated crude homogenate than in a 50-fold dilution of the crude homogenate. This concentration dependence was lost after extensive purification of the mutant adenylate kinase, although the enzyme was still thermolabile. A protein was identified that co-purified with the wild type and mutant enzyme through several purification steps and that altered the degree of thermolability of the mutant adenylate kinase. A homogeneous preparation of the adenylate kinase-associated protein gave a single band on a sodium dodecyl sulfate-polyacrylamide gel with Mr = 34,000. The interaction of this protein with adenylate kinase explains why the thermolability of the mutant adenylate kinase changed during purification and the dependence of the thermolability on concentration. The adenylate kinase-associated protein may be important in regulating the activity of adenylate kinase and subsequently affecting the rate of cell growth.