R. E. Barden, W. Cleland
Jul 10, 1969
Citations
1
Influential Citations
124
Citations
Quality indicators
Journal
The Journal of biological chemistry
Abstract
Abstract The substrate specificity of 1-acylglycerol 3-phosphate acyltransferase from rat liver microsomes for both acylcoenzyme A and 1-acylglycerol 3-phosphate has been determined at levels below the critical micelle concentrations of the substrates. The fatty acid of the acylglycerol 3-phosphate is not important, but for the acyl-CoAs the specificity is oleyl g palmitoleyl ≃ linoleyl ≃ palmityl g myristyl g stearyl g lauryl. 1-Acylglycerol 3-phosphate acyltransferase appears to work only with monomeric substrates. The Km for palmityl-CoA is less than 0.1 µm, while the Km values for the 1-acylglycerol 3-phosphates are in the low micromolar range (5 to 25 µm), but are difficult to measure accurately because micelles form at 4 to 8 µm 1-acylglycerol-3-P and the velocity ceases to increase. By contrast, acyl-CoA hydrolase appears to prefer micelles as substrate. This enzyme shows little activity at 3 µm acyl-CoA, and shows 8 times more activity with palmityl-CoA than with any other acyl-CoA tested. In order to plan the specificity studies, the critical micelle concentrations of the acyl-CoAs and 1-acylglycerol 3-phosphates used were determined by the dye adsorption technique with pinacyanol chloride. For acyl-CoAs in 6.7 mm phosphate, 10 mm K+, pH 6.9, the values were: lauryl, 9.5 µm; myristyl, 4 µm; palmityl, 3.6 (4 µm in 50 mm Tris-HCl, pH 7.4; 6 µm in deionized water); palmitoleyl, 2 µm; stearyl, 2 µm; oleyl, 4.5 µm; linoleyl, 5.5 µm. For 1-acylglycerol 3-phosphates in 50 mm Tris-HCl, pH 7.4, the values were: myristyl, 120 µm; palmityl, 35 µm; stearyl, 7 µm; oleyl, 23 µm; linoleyl, 34 µm; 1-acylglycerol 3-phosphate prepared from egg lecithin (80% palmitic), 37 µm.