Acyl specificity in triglyceride synthesis by lactating rat mammary gland.
We have studied the specificity of the acyl-CoA:diglyceride acyltransferase reaction in lactating rat mammary gland to provide a rational explanation at the enzyme level for the nonrandom distribution of fatty acids in milk fat triglycerides. Acyl-CoA:diglyceride acyltransferase activity was measured using various diglyceride and radioactive acyl-CoA substrates; products were identified as triglycerides by thin-layer and gas-liquid chromatography. Most of the enzymatic activity was located in the microsomal fraction and showed a broad specificity for the acyl donors tested C10, C12, C14, C16, C18, and C18:1 CoA esters). The acyltransferase activity was highly specific for sn-1,2-diglyceride enantiomers; rac-1,3- and sn-2,3-diglycerides were relatively inactive. The acyl-CoA specificity was not affected by the type of 1,2-diglyceride acceptor offered, although dilaurin was the best acceptor and sn-1,2-dilaurin greater than sn-1,2-dimyristin greater than sn-1,2-dipalmitin greater than sn-1,2-distearin. We have previously shown that in the microsomal fraction from lactating rat mammary gland, the acyltransferase activities concerned with the conversion of sn-glycero-3-phosphate to diacylglycerophosphate show a very marked specificity for long chain acyl-CoA's. Therefore, we conclude that the predominant localization of long chain fatty acids in the 1 and 2 positions, and of shorter chain fatty acids in the 3 position of the glycerol backbone, results at least in part from the specificities of the mammary gland acyltransferases.
D000217:Acyltransferases / Q000378:metabolism; D000818:Animals; D002849:Chromatography, Gas; D004075:Diglycerides / Q000378:metabolism / Q000494:pharmacology; D005260:Female; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007774:Lactation; D008321:Mammary Glands, Animal / Q000378:metabolism*; D011247:Pregnancy; D051381:Rats; D013329:Structure-Activity Relationship; D013347:Subcellular Fractions / Q000201:enzymology; D014280:Triglycerides / Q000096:biosynthesis*
D004075:Diglycerides; D014280:Triglycerides; D000217:Acyltransferases