Properties of a Zn(2+)-glycerophosphocholine cholinephosphodiesterase from bovine brain membranes.
A Zn(2+)-glycerophosphocholine cholinephosphodiesterase was purified with a specific activity of 4.6 mumole/min.mg protein from bovine brain membranes by procedures involving PI-PLC solubilization, concanavalin A affinity chromatography, CM-sephadex chromatography and Sephadex G-150 chromatography. Based on molecular weight determination gel chromatography and SDS polyacrylamide gel electrophoresis, the phosphodiesterase activity appears to be a dimeric protein (110 kDa) composed of two subunits with a molecular weight of approximately 54 kDa. The K(m) value for p-nitrophenylphosphocholine and the optimum pH were found to be 16 microM and pH 10.5, respectively. The phosphodiesterase was inhibited by Cu2+, but not the other divalent metal ions. The activity of the apoenzyme was remarkably activated by Co2+ or Zn2+, but not Mn2+ or Mg2+. In addition, the inactivation of the enzyme in glycine buffer was prevented by Mn2+ or Zn2+, but not Co2+ or Mg2. In a separate experiment, comparing properties of the purified and membrane-bound phosphodiesterases, the forms of two enzymes were quite similar except in stability. Both enzymes were more stable at pH 7.4 than pH 5 or 10. However, the membrane-bound enzyme was more stable than the soluble enzyme at all three pHs. These data suggest that the activity of the phosphodiesterase may be stabilized in-vivo.
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College of Pharmacy, Chungnam National University, Yuseong-Ku, Taejon, Korea.
D000818:Animals; D001921:Brain / Q000201:enzymology* / Q000648:ultrastructure; D002417:Cattle; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D016014:Linear Models; D008566:Membranes / Q000201:enzymology; D008970:Molecular Weight; D010727:Phosphoric Diester Hydrolases / Q000737:chemistry*; D013696:Temperature
D010727:Phosphoric Diester Hydrolases; C061931:glycerophosphocholine cholinephosphodiesterase