Candida utilis NAD+ kinase: kinetic and inhibition studies with ADP.

1. Initial velocity and product inhibition studies using ADP were carried out on cytoplasmic NAD+ kinase (ATP:NAD 2' phosphotransferase, EC 2.7.1.23) purified from Candida utilis. Initial velocity studies were also carried out on a sample of chicken liver NAD+ kinase. 2. The data indicate both enzymes followed a sequential mechanism of reactant binding. 3. Product inhibition studies on C. utilis NAD+ kinase suggest the mechanism of NAD+, ATP addition is best described as rapid equilibrium random with multiple binding of ADP to the free enzyme and the E X ATP and E X NAD+ complexes. 4. The characteristics of this enzyme, prepared from several sources, are briefly summarized.