Cold acclimation increases activities of mitochondrial long-chain acyl-CoA synthetase and carnitine acyl-CoA transferase I in heart of rainbow trout (Oncorhynchus mykiss)

Abstract

Rainbow trout (Oncorhynchus mykiss) were acclimated to 5 or 15 °C. Hearts were excised and assayed for the activity of enzymes essential for fatty acid metabolism. The activity of long-chain acyl-CoA synthetase, the first enzyme required in either fatty acid oxidation or complex fatty acid synthesis, was increased following acclimation to low temperature. Total crude homogenates exhibited an increase in activity with either palmitate (0.037–0.047 μmol/(min∙g)), stearate (0.037–0.055 μmol/(min∙g)), or oleate (0.041–0.064 μmol/(min∙g)) as substrate. Mitochondrial preparations showed the greatest increase in activity with palmitate (0.486–0.962 nmol/(min∙g)) as substrate, whereas microsomal preparations exhibited the greatest increase in activity with oleate (0.976–1.933 nmol/(min∙g)) as substrate. The activity of carnitine acyl-CoA transferase I, which is located on the outer mitochondrial membrane and is required for fatty acid oxidation, increased following acclimation to low temperature with palmitoyl CoA (0.137–0.352 μmol/(min∙g)), stearoyl CoA (0.066–0.152 μmol/(min∙g)), or oleoyl CoA (0.137–0.224 μmol/(min∙g)) as substrate. The parallel increase in mitochondrial long-chain acyl-CoA synthetase and carnitine acyl-CoA transferase I is consistent with previous observations of an elevated capacity of heart to oxidize fatty acids as exogenous fuels following acclimation to low temperature. The increase in microsome-based long-chain acyl-CoA synthetase may contribute to heart growth at low temperature.