Mechanism of action of cobalt ions on rat osseous plate alkaline phosphatase.

Polidocanol-solubilized osseous plate alkaline phosphatase was modulated by cobalt ions in a similar way as by magnesium ions. For concentrations up to 1 microM, the Chelex-treated enzyme was stimulated by cobalt ions, showing Kd = 6.0 microM, V = 977.5 U/mg, and site-site interactions (n = 2.5). Cobalt-enzyme was highly unstable at 37 degrees C, following a biphasic inactivation process with inactivation constants of about 0.0625 and 0.0015 min-1. Cobalt ions stimulated the enzyme synergistically in the presence of magnesium ions (Kd = 5.0 microM; V = 883.0 U/mg) or in the presence of zinc ions (Kd = 75.0 microM; V = 1102 U/mg). A steady-state kinetic model for the modulation of enzyme activity by cobalt ions is proposed.