Journal of Lipid Research, Vol. 13, 348-355, May 1972
Copyright © 1972 by Lipid Research, Inc.

Characterization of glycerophosphorylcholine, -ethanolamine, -serine, -inositol, and -glycerol hydrolytic activity in housefly larvae

G. R. Hildenbrandt and L. L. Bieber

Department of Biochemistry, Michigan State University, East Lansing, Michigan 48823

Homogenates of Musca domestica (housefly) larvae contain glycerophosphodiesterase activity, which is found in the supernatant fluid after centrifugation at 88,000 g. The phosphodiesterase is inhibited by EDTA and is stimulated by Mg²⁺, Ni²⁺, Co²⁺, and Mn²⁺. The pH optimum is 7.2. The enzyme is stable to heating at 50°C for 15 min and is insensitive to sulfhydryl inhibitors. Glycerophosphoryl diesters of choline, ethanolamine, inositol, serine, glycerol, and ßbeta;-methylcholine are hydrolyzed to the common product, l--glycerophosphate, and the appropriate free alcohol. The rate of glycerophosphorylcholine hydrolysis is 70% greater than the rate of hydrolysis of the other glycerophosphodiesters. Apparent K_m values for glycerophosphorylcholine, glycerophosphorylethanolamine, and glycerophosphoryl-ßbeta;-methylcholine are 2-4 x 10^-4 m, and for glycerophosphorylinositol, 2 x 10^-3 m. Competitive studies using various pairs of substrates, as well as the exchange of free choline into both glycerophosphorylcholine and glycerophosphorylinositol, suggest that a single enzyme cleaves all substrates. Product inhibition and reversal of the reaction were not detected. Choline, but not l--glycerophosphate, exchanges into glycerophosphorylcholine and glycerophosphorylinositol.

Supplementary key words glycerophosphodiesterase

Submitted on October 26, 1971
Accepted on December 27, 1971

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