Phosphorylated intermediate of alkaline phosphatase.

We have measured the phosphorylation of the subunits of alkaline phosphatase in the steady state with several substrates and at several pH values. Our results vary from 80% phosphorylation of both subunits at pH7 to only 9% at pH 10. There is no evidence of anticooperativity. With the measurement of kcat, we are able to evaluate rate constants in a minimal scheme. The results show that the main rate influencing steps ar chemical dephosphorylation and dissociation of phosphate. The predominates at pH 7.0 but declines in importance as the pH is raised. Our rate constants for dissociation of phosphate are in agreement with recent NMR studies.