engleski

Metal-ion Dependent Asymmetry of Alkaline Phosphatase

Alkaline phosphatase is nonspecific fosfomonoesterase catalysing phosphohydrolytic and phosphoryl-transfer reactions. Biological function of ALP is still unclear. The widespread occurence of ALP in nature implicates involvment in fundamental biological processes, most likely in phosphate transport. Alp is multimeric metalloprotein with three metal ion binding sites pewr active site. Two zinc ions directly participate in substrate binding and catalysis while the role of the magnesium ion is not fully understod yet. Alp shows deviations from Michaelis-Menten kinetics what could be substantiated by a model assuming nonequivalent subunits. It has been reported that Alp from E.coli is not fully saturated with magnesium ions. Unequal saturation of the subunits could induce observed enzyme asymmetry. The dependence of the kinetic constants and deviations from Michaelis-Menten kinetics on the magnesium concentration has been investigated. The difference in subunit affinity for ligands as well as deviations from linearity are reduced in the presence of higher Mg 2+ concentration, as could be expected upon binding of Mg 2+ to both subunits. It has been established by limited proteolysis that difference in tertiary structure exists between enzymes of variable saturation with metal ions. Obtained results could provide insight in the role of ALP in the phosphate transport.

subunit interaction; metal ion; alkaline phosphatase

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