Abstract
Abstract The shape of an Arrhenius plot of glycerol 3-phosphate acyltransferase activity of an unsaturated fatty acid auxotroph of Escherichia coli is identical in membranes containing cis-vaccenic, oleic, linoleic, or linolenic acid as sole unsaturated fatty acid. The curve is linear at low temperatures with a continuous decrease in slope above 15°. In membranes containing trans-unsaturated fatty acids as the sole unsaturated fatty acid, the decrease in slope occurs at 20°. Membranes from cells grown in the presence of oleic acid and then grown for one generation in the absence of unsaturated fatty acids contained 79% saturated fatty acids and 21% oleic acid. Temperature dependence of the enzyme activity in these membranes was intermediate between that observed in membranes containing trans-unsaturated fatty acids and those containing normal amounts of cis-unsaturated fatty acids. 1-Acylglycerol 3-phosphate acyltransferase activity exhibited a linear Arrhenius plot identical in slope in membranes containing cis-unsaturated fatty acids of varying degrees of unsaturation. Membranes from cells deprived of unsaturated fatty acids for one generation or those containing trans-unsaturated fatty acids exhibited a steeper slope. Membranous glycerol 3-phosphate dehydrogenase activity appeared to be independent of membrane fatty acid composition. Linear Arrhenius plots of identical slope were observed in all membrane preparations described above. The difference in the dependence of the temperature characteristics of various membranous enzymes on membrane fatty acid composition suggests a heterogeneity in the relationship between membranous enzymes and membrane phospholipids.
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