The Kinetic Properties of Oleoyl-CoA:1-Acyl-sn-glycero-3-phosphocholine O-Acyltransferase from Mouse-Brain Microsomes

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Abstract
The kinetic properties of acylation of 1-acyl-sn-glycero(-3)phosphocholine by oleoyl-CoA were examined using mouse brain microsomes. The enzyme-catalyzed reactions were studied by measuring the rate of reaction while systematically varying the concentrations of oleoyl-CoA and 1-acylglycerophosphocholine. Double reciprocal plots of velocity vs. 1-acylglycerophosphocholine produced a family of parallel lines, and similar plots for oleoyl-CoA produced a family of parallel curves. Inhibition was observed at high concentrations of either substrate. By extrapolation from low substrate concentrations, the Vmax for oleoyl-CoA:1-acylglycerophosphocholine acyltransferase in brain microsomes was 6.1 nmol min-1 mg-1, and Km values were determined to be 11 .mu.M and 107 .mu.M for oleoyl-CoA and 1-acylglycerophosphocholine, respectively. Similar results were obtained for the enzyme-catalyzed transfer of oleoyl groups to 1-acyl-sn-glycerophosphoinositol. Vmax was 2.1 nmol min-1 mg-1 and the Km values were 4 .mu.M and 14 .mu.M for oleoyl-CoA and 1-acylglycerophosphoinositol, respectively. The mechanistic implications of the kinetic properties of the acyltransferases with respect to acyl group specificity for the phosphoglycerides in brain microsomes are discussed.

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