The inhibition of acetate, pyruvate, and 3-phosphogylcerate kinases by chromium adenosine triphosphate.

The inert coordination complex, chromium ATP, has been used to study the steady state kinetic mechanisms of acetate, pyruvate, and d-phosphoglycerate kinases. With pyruvate and 3-phosphoglycerate kinases, CrATP competes with both substrates and has a dissociation constant of 200 pM. This behavior is consistent with a random sequential mechanism for these enzymes. The fact that saturation with the nonnucleotide substrate eliminates most or all of the CrATP inhibition makes these enzymes useful as coupling enzymes (together with lactate dehydrogenase or glyceraldehyde-P dehydrogenase) in assays for other kinases when CrATP inhibition is being studied. With acetate kinase, CrATP competes with MgATP and is noncompetitive Versus acetate. As a product inhibitor, acetyl phosphate is noncompetitive versus either MgATP or acetate. Initial velocity studies show the enzyme to have a sequential mechanism. A random mechanism is proposed which accounts for the kinetic data, and for the isotope exchanges and the phosphoenzyme isolated by other workers.