Asymmetric distribution of decanoate in triacylglycerol synthesized in vitro by mammary glands of lactating mice.

Slices, prepared from the mammary glands of lactating mice, were incubated with either [1-14C]acetate, [U-14C]glucose, or [1-14C]decanoate. From all 3 substrates, radioactivity in the synthesized lipids was found mainly in triacylglycerols (TG). When acetate or glucose served as substrate, decanoate (C10) accounted for 24% of the fatty acids in TG. Hydrolysis of the TG by pancreatic lipase yielded [14C] fatty acids which had relatively more C10 (38%) than did either of the other hydrolysis products mono- or diacylglycerol (14-17%). However, when TG produced by slices from C10 were hydrolyzed, the acid was found to be esterified equally at the C-1, C-2 and C-3 of glycerol. Thus, when fatty acids are synthesized de novo and are converted to TG by gland slices, C10 is predominantly located in the C-3 position, a finding in accord with the situation in milk TG, although such preferential incorporation does not occur when the free acid is presented to the tissue slices.