RAT OSSEOUS PLATE ALKALINE-PHOSPHATASE - MECHANISM OF ACTION OF MANGANESE IONS

Polidocanol-solubilized osseous plate alkaline phosphatase was modulat ed by manganese ions in a similar way as by zinc ions. For concentrati ons up to 1.0 nM, the enzyme was stimulated by manganese ions, showing site-site interactions (n = 2.2). However, larger concentrations (> 0 .1 mu M) were inhibitory. Manganese ions could play the role of zinc i ons stimulating the enzyme synergistically in the presence of magnesiu m ions (K-d = 7.2 mu M; V = 1005.5 U mg(-1). Manganese ions could also play the role of magnesium ions, stimulating the enzyme synergistical ly in the presence of zinc ions (K-d = 2.2 mu M; V = 1036.7 U mg(-1). However, manganese ions could not substitute for zinc and magnesium at the same time since ion assymetry is necessary for full activity of t he enzyme. A steady-state kinetic model for the modulation of enzyme a ctivity by manganese ions is proposed.