title: Activation of sphingomyelinase from Bacillus cereus by Zn2+ hitherto accepted as a strong inhibitor.
abstract: Sphingomyelinase (SMase) from Bacillus cereus has been known to be activated by Mg2+, Mn2+, and Co2+, but strongly inhibited by Zn2+. In the present study, we investigated the effects of several kinds of metal ions on the catalytic activity of B. cereus SMase, and found that the activity was inhibited by Zn2+ at its higher concentrations or at higher pH values, but unexpectedly activated at lower Zn2+ concentrations or at lower pH values. This result indicates that SMase possesses at least two different binding sites for Zn2+ and that the Zn2+ binding to the high-affinity site can activate the enzyme, whereas the Zn2+ binding to the low-affinity site can inactivate it. We also found that the binding of substrate to the enzyme was independent of the Zn2+ binding to the high-affinity site, but was competitively inhibited by the Zn2+ binding to the low-affinity site. The binding affinity of the metal ions to the site for activating the enzyme was determined to be in the rank-order of Mg2+ = Co2+ < Mn2+ < Zn2+. It was also demonstrated that these four metal ions competed with each other for the same binding site on the enzyme molecule.
authors.affiliation: Department of Biochemistry, Osaka University of Pharmaceutical Sciences, 4-20-1 Nasahara, Takatsuki, Osaka 569-1094, Japan.
authors.forename: Shinobu
authors.initials: S
authors.lastname: Fujii
authors.forename: Hiromi
authors.initials: H
authors.lastname: Itoh
authors.forename: Ayumi
authors.initials: A
authors.lastname: Yoshida
authors.forename: Satoko
authors.initials: S
authors.lastname: Higashi
authors.forename: Hiroh
authors.initials: H
authors.lastname: Ikezawa
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Ikeda
mesh_terms: D001409:Bacillus cereus / Q000737:chemistry*; D001665:Binding Sites; D002384:Catalysis; D002712:Chlorides / Q000494:pharmacology; D003035:Cobalt / Q000737:chemistry; D003300:Copper / Q000737:chemistry; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007477:Ions; D007700:Kinetics; D008345:Manganese / Q000737:chemistry; D008954:Models, Biological; D008956:Models, Chemical; D011485:Protein Binding; D013108:Sphingomyelin Phosphodiesterase / Q000037:antagonists & inhibitors / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*; D017967:Zinc Compounds / Q000494:pharmacology
chemical_list: D002712:Chlorides; D007477:Ions; D017967:Zinc Compounds; D003035:Cobalt; D008345:Manganese; D003300:Copper; C016837:zinc chloride; D013108:Sphingomyelin Phosphodiesterase; C018021:cobaltous chloride; D015032:Zinc