MECHANISM OF ACTION OF COBALT IONS ON RAT OSSEOUS PLATE ALKALINE-PHOSPHATASE

Polidocanol-solubilized osseous plate alkaline phosphatase was modulat ed by cobalt ions in a similar way as by magnesium ions. For concentra tions up to 1 mu M, the Chelex-treated enzyme was stimulated by cobalt ions, showing K-d = 6.0 mu M, V = 977.5 U/mg, and site-site interacti ons (n = 2.5). Cobalt-enzyme was highly unstable at 37 degrees C, foll owing a biphasic inactivation process with inactivation constants of a bout 0.0625 and 0.0015 min(-1). Cobalt ions stimulated the enzyme syne rgistically in the presence of magnesium ions (K-d = 5.0 mu M; V = 883 .0 U/mg) or in the presence of zinc ions (K-d = 75.0 mu M; V = 1102 U/ mg). A steady-state kinetic model for the modulation of enzyme activit y by cobalt ions is proposed.