Anomalous stimulation of Escherichia coli alkaline phosphatase activity in guanidinium chloride. Modulation of the rate-limiting step and negative cooperativity.

Guanidinium chloride stimulates the activity of alkaline phosphatase from Escherichia coli, by 3-4-fold. Structural parameters of the enzyme, monitored by fluorescence and circular dichroism, indicate progressive denaturation. This unusual stimulation is shown to be independent of the nature of the substrate and source of the enzyme. Profiles of pH dependence and transphosphorylation reaction indicate that the dephosphorylation step of the catalysis is enhanced in the presence of guanidinium chloride. We demonstrate, by fast-flow kinetics and inhibitor titrations, that guanidinium chloride enhances activity by abolishing negative cooperativity and by accelerating the dissociation of rate-limiting enzyme and substrate (E.P) complex.