The role of acyltransferases in fatty acid utilization

Glycerophosphate and carnitine as competing acyl acceptors and the oxidation of different long chain acylcarnitines in isolated mitochondria have been investigated. In the presence of low concentrations of palmitate, glycerophosphate is the preferred acyl acceptor in isolated liver mitochondria, indicating that the glycerophosphate acyltransferase has a lower Michaelis constant (Km) for palmityl-CoA than has the carnitine palmityltransferase. Liver mitochondria from starved rats make more palmitylcarnitine and less palmitylglycerophosphate than do mitochondria from starved/refed rats. In heart mitochondria glycerophosphate has less effect on palmitylcarnitine formation because of glycerophosphate acyltransferase activity is lower and the carnitine palmityltransferase activity is higher in liver mitochondria. Carnitine esters of C22 fatty acids, especially erucic acid (22:1omega9,cis) are more slowly oxidized compared to palmitylcarnitine in heart than in liver mitochondria. They also inhibit palmitylcarnitine oxidation. The inhibition is relatively stronger in heart than in liver mitochondria. These observations are discussed in relation to organ differences in the utilization of fatty acids.