Stereospecificity of monoacylglycerol and diacylglycerol acyltransferases from rat intestine as determined by chiral phase high‐performance liquid chromatography

Using chiral phase high‐performance liquid chromatography of diacylglycerols, we have redetermined the ratios of 1,2‐/2,3‐diacyl‐ sn ‐glycerols resulting from acylation of 2‐monoacylglycerols by membrane bound and solubilized triacylglycerol systhetase of rat intestinal mucosa. With 2‐oleoyl[‐ 3 H]glycerol as the acyl acceptor and oleoyl‐CoA as the acyl donor, 97–98% of the diacylglycerol product was 1,2(2,3)‐dioleoyl‐ sn ‐glycerol, 90% of which was the sn ‐1,2‐and 10% the sn ‐2,3‐enantiomer. The remaining diacylglycerol (less than 3%) was the sn ‐1,3‐isomer. The overall yield of acylation products was 70%, of which 60% were diacylglycerols and 40% triacylglycerols. With 2‐oleylglycerol ether as the acyl acceptor and [1‐ 14 C]oleoyl‐CoA as the acyl donor, 90% of the diradylglycerol was 1‐oleoyl‐2‐oleyl‐ sn ‐glycerol and 10% was the 2‐oleyl‐3‐oleoyl‐ sn ‐glycerol. The diradylglycerols made up 96% and the triradylglycerols 4% of the radioactive product. With 1‐palmitoyl‐ sn ‐glycerol as the acyl acceptor and [1‐ 14 C]oleoyl‐CoA as the acyl donor, the predominant reaction product was 1‐palmitoyl‐3‐oleoyl‐ sn ‐glycerol. The 3‐palmitoyl‐ sn ‐glycerol was not a suitable acyl acceptor. Both 1,2‐ and 2,3‐diacyl‐ sn ‐glycerols were substrates for diacylglycerol acyltransferase as neither isomer was favored when 1,2‐dioleoyl‐ rac ‐[2‐ 3 H]glycerol was used as the acyl acceptor. There was a marked decrease in the acylation of the 1(3)‐oleoyl‐2‐oleyl‐ sn ‐glycerol to the 1,3‐dioleoyl‐2‐oleyl‐ sn ‐glycerol. It is concluded that neither monoacylglycerol nor diacylglycerol acyltransferase exhibit absolute stereospecificity for acylglycerols as fatty acid acceptors.