Although it is rapidly metabolized in cultured rat hepatocytes, lauric acid is used for protein acylation

Abstract

This study was designed to examine the metabolic fate of exogenous lauric acid in cultured rat hepatocytes, in terms of both lipid metabolism and acylation of proteins. Radiolabeled [1-14C]-lauric acid at 0.1 mM in the culture medium was rapidly taken up by the cells (94.8 ± 2.2% of the initial radioactivity was cleared from the medium after a 4 h incubation) but its incorporation into cellular lipids was low (24.6 ± 4.2% of initial radioactivity after 4 h), due to the high β-oxidation of lauric acid in hepatocytes (38.7 ± 4.4% after the same time). Among cellular lipids, lauric acid was preferentially incorporated into triglycerides (10.6 ± 4.6% of initial radioactivity after 4 h). Lauric acid was also rapidly converted to palmitic acid by two successive elongations. Protein acylation was detected after metabolic labeling of the cells with [11, 12-3H]-lauric acid. Two-dimensional electrophoresis separation of the cellular proteins and autoradiography evidenced the incorporation of radioactivity into 35 well-resolved proteins. Radiolabeling of several proteins resulted from covalent linkage to the precursor [11,12-3H-lauric acid or to its elongation product, myristic acid. The covalent linkages between these proteins and lauric acid were broken by base hydrolysis, indicating that the linkage was of the thioester or ester-type. Endogenous myristic acid produced by lauric acid elongation was used for both protein N-myristoylation and protein S-acylation. Therefore, these results show for the first time that, although it is rapidly metabolized in hepatocytes, exogenous lauric acid is a substrate for the acylation of liver proteins.