Control of lipid metabolism in adipose-tissue homogenates of fasted refed rats.

Abstract

The 700 ×g fat‐poor internatant from epididymal adipose tissue homogenate of fasted refed rats was incubated at pH 6.5 with 0.5 mM [1‐14C]acetate in the presence of cofactors. After incubation, six lipid classes were separated by thin‐layer chromatography and their fatty acids analyzed by radio gas‐liquid chromatography. The incorporation of [1‐14C]acetate into glycerides was limited by the activity of acetyl‐CoA carboxylase, and was stimulated two to three‐fold by the addition of 0.1 mM unlabelled malonyl‐CoA. The chain‐length of fatty acids labelled in vitro was controlled by the relative concentrations of malonyl‐CoA and acetyl‐CoA. Addition of unlabelled malonyl‐CoA influenced the operation of fatty acid synthetase in such a way that the ratio of radioactive palmitate to radioactive myristate increased markedly. sn‐Glycerol 3‐phosphate stimulated the esterification of fatty acids into triglycerides. Under these conditions whereas the specific activity of free fatty acids was much higher than that observed in triglycerides, the specific activity of diglycerides was low, when compared to the same triglycerides. Newly synthesized monounsaturated fatty acids were preferentially esterified into triglycerides. 0.5 mM [1‐14C]palmitate was efficiently incorporated into triglycerides but not into diglycerides.