Effects of Temperature on the Oxidation of Fatty Acids, Acyl Carnitines, and Ketone Bodies by Mitochondria Isolated from the Liver of the Lake Charr,Salvelinus namaycush

Abstract

Mitochondria isolated from the liver of the Lake Charr Salvelinus namaycush oxidize a wide range of acyl chain lengths of fatty acids and acyl carnitines at 1, 10, and 20 °C. For most carbon chain lengths the relative importance of carnitine-dependent fatty acid oxidation increases with increasing temperature due to greater thermal enhancement of carnitine-dependent oxidation. At low temperatures the rate of carnitine-independent fatty acid oxidation rivals that of carnitine-dependent oxidation. Therefore, acute temperature shifts during excursions above the thermocline would have important effects on the oxidation of dietary and depot lipids. Temperature does not substantially affect the chain length preference for fatty acid oxidation either in the presence or absence of carnitine, suggesting acclimation-induced changes in substrate specificity of fatty acid oxidation may not be necessary. The importance of β-hydroxybutyrate as an oxidative substrate increases at low temperatures relative to other substrates while acetoacetate oxidation is greater than that of β-hydroxybutyrate at 10 and 20 °C. Altered ketone body metabolism may play a role in regulating cholesterol levels to alter membrane fluidity.