Properties of inosinic acid dehydrogenase from Bacillus subtilis. II. Kinetic properties.

Abstract

Some of the kinetic properties of inosine 5′-phosphate (IMP) dehydrogenase purified from Bacillus subtilis have been described. K+ can be replaced as an activator by other monovalent cations, whose activities are related to their ionic radii. IMP dehydrogenase is stimulated by appropriate concentrations of adenosine 5′-phosphate, and is strongly inhibited by the antibiotic mycophenolic acid. The enzyme is inhibited by guanosine 5′-phosphate (GMP), a suspected negative feedback inhibitor, in a complex manner. Desensitization of this inhibition suggests that GMP binds at a site distinct from the catalytic site. Several properties of the enzyme change after desensitization. For example, the pH optimum shifts from pH 7.55 to pH 8.4, and whereas the inhibition by GMP is greatly reduced there is an increase in catalytic activity. These studies and the oligomeric structure of IMP dehydrogenase strongly indicate a regulatory role for the enzyme in B. subtilis.