title: Effects of metal ions on sphingomyelinase activity of Bacillus cereus.
abstract: Some divalent metal ions were examined for their effects on sphingomyelinase activity of Bacillus cereus. The enzyme activity toward mixed micelles of sphingomyelin and Triton X-100 proved to be stimulated by Co2+ and Mn2+, as well as by Mg2+. Km's for Co2+ and Mn2+ were 7.4 and 1.7 microM, respectively, being smaller than the Km for Mg2+ (38 microM). Sr2+ proved to be a competitive inhibitor against Mg2+, with a Ki value of 1 mM. Zn2+ completely abolished the enzyme activity at concentrations above 0.5 mM. The concentration of Zn2+ causing 50% inhibition of the enzyme activity was 2.5 microM. Inhibition by Zn2+ was not restored by increasing concentrations of Mg2+ when the concentration of Zn2+ was above 10 microM. Ba2+ was without effect. When sphingomyelinase was incubated with unsealed ghosts of bovine erythrocytes at 37 degrees C, the enzyme was significantly adsorbed onto the membrane in the presence of Mn2+, Co2+, Sr2+ or Ba2+. Incubation with intact or Pronase-treated erythrocytes caused enzyme adsorption only in the presence of Mn2+. In the course of incubation, the enzyme was first adsorbed on the membranes of intact bovine erythrocytes in the presence of Mn2+; then sphingomyelin breakdown proceeded with ensuing desorption of adsorbed enzyme. Hot-cold hemolysis occurred in parallel with sphingomyelin breakdown. In this case, the hydrolysis of membranous sphingomyelin as well as the initial enzyme adsorption took place in the following order: unsealed ghosts greater than Pronase-treated erythrocytes greater than intact erythrocytes.
mesh_terms: D000818:Animals; D001409:Bacillus cereus / Q000201:enzymology*; D002413:Cations, Divalent / Q000494:pharmacology; D002417:Cattle; D004789:Enzyme Activation / Q000187:drug effects; D004910:Erythrocyte Membrane / Q000378:metabolism; D007700:Kinetics; D008670:Metals / Q000494:pharmacology*; D008823:Micelles; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D013108:Sphingomyelin Phosphodiesterase / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D002413:Cations, Divalent; D008670:Metals; D008823:Micelles; D010727:Phosphoric Diester Hydrolases; D013108:Sphingomyelin Phosphodiesterase