The role of chain elongation systems in the supplying of fatty acids to the adipocyte membrane lipids.

A study of the fatty acid composition of the subcellular membranes and of the storage vacuole lipids of rat adipocytes indicated that the proportions of palmitic, stearic, oleic, linoleic and arachidonic acids of the total membrane lipids are essentially the same, while the storage fat is characterized by a higher proportion of oleate (31.5%), a lower proportion of stearate (3.7%) and by the absence of arachidonate. Adipocyte homogenate was incubated under conditions allowing for de novo synthesis, activation, elongation and esterification of fatty acids and the different subcellular fractions were then separated. Part of the newly synthesized fatty acids were found to be incorporated into the adipocyte membranes. The percentage of total fatty acid activity in the carboxyl was found to be 2.7, 2.4, 2.2 and 1.3 times greater, respectively, than the theoretical de novo synthesis value in plasma membranes, microsomes, mitochondria and supernatant. This suggests a functional relationship between elongation of fatty acids and their incorporation into the adipocyte subcellular membranes. The results of experiments in which fatty acid activation cofactors were omitted from the medium indicate that the membranous fatty acid elongation system, unlike fatty acid synthetase, is devoid of deacylase activity.