Deacylation and uptake of the fatty acyl chain from enantiomeric dialkylacylglycerol by intact rat fat cells.

Isolated rat fat cells hydrolyze the ester bond in position 3 of enantiomeric dialkyl[3H]acylglycerol added as triester-analogue substrate. This lipolytic system constitutes an integrated model which allows, in the absence of di- and monoesters, specific determinations of both the rate-limiting step in triacylglycerol breakdown and the uptake of acyl residues in cell lipids. Splitting of the ester bond was catalyzed by a cell-bound acylhydrolase which exhibited the characteristic properties of lipoprotein lipase. About 70% of the total amount of 3H-labelled fatty acid released during hydrolysis were concomitantly taken up by the cells and reesterified, mainly as triacylglycerol, in cell lipids. The acyl residues appeared to penetrate the cells directly after lipoprotein lipase hydrolysis, without entering the extracellular compartment. This, along with previous finding of a high positive correlation between rates of lipolytic activity and fatty acid uptake (Vérine, A., Salers, P. and Boyer, J. (1982) Am. J. Physiol. 243, E175-E181), suggests that the uptake process is directly related to enzyme action. These results are consistent with the concept that lipoprotein lipase, besides being an acylhydrolase, could also function as acyltransferase.