Acyl-CoA synthase and acyltransferase activity in developing skeletal muscle membranes

Enzymes participating in the activation and esterification of fatty acids for complex lipid biosynthesis were characterized in neonatal and adult rabbit skeletal muscle membranes. The activity of acyl-CoA synthase was 1.4-1.6-fold greater in neonatal vs. adult sarcoplasmic reticulum for the fatty acid substrates linoleic (2.6 vs. 1.61 nmol 18:2-CoA/min per mg), stearic (0.94 vs. 0.66 nmol 18:0-CoA/min per mg) and palmitic (2.43 vs. 1.51 nmol 16:0-CoA/min per mg) acids. Enzyme activity was identical between neonate and adult for coenzyme A, ATP and linoleic acid concentration dependence. Glycerol-3-phosphate Acyltransferase activity was 6-fold greater in neonatal than adult sarcoplasmic reticulum for both linoleoyl-CoA (1.4 vs. 0.22 nmol 18:2/min per mg) and stearoyl-CoA (1.1 vs. 0.13 nmol 18:0/min per mg) donor substrates, whereas lysophosphatidylcholine Acyltransferase activity was similar. Enriched fractions of sarcolemmal membranes possessed the highest activity for lysophosphatidylcholine Acyltransferase activity, being 2-4-fold greater than sarcoplasmic reticulum. In contrast to sarcoplasmic reticulum, lysophosphatidylcholine Acyltransferase activity was 2-3-fold greater in neonatal compared to adult sarcolemma for lineoleic (18.9 vs. 8.5 nmol 18:2/min per mg) and the stearic (2.8 vs. 0.68 nmol 18:0/min per mg) acid incorporation. The greater capacity of neonatal membranes for acylation by the de novo pathway is in accord with the requirements for neonatal muscle to effect high rates of triacylglycerol and phospholipid synthesis essential for oxidative metabolism and membrane synthesis during postnatal development and growth.