Selective utilization of fatty acids in rainbow trout (Oncorhynchus mykiss Walbaum) red muscle mitochondria

Abstract

This study was undertaken to establish whether fatty acids are generally oxidized at the same rate or if a pattern of oxidation rates exists to protect certain fatty acids from degradation for ATP formation. Beta-oxidation was studied in red muscle mitochondria of 10 major fatty acids that are acquired in the diet and occur in the fat depots of rainbow trout (Oncorhynchus mykiss Walbaum). The mitochondria were isolated by fractional centrifugation and the fatty acids were added as coenzyme A esters in the presence of carnitine. The fatty acids could be separated into roughly three groups in relation to their oxidation rates. Two fatty acids (14:0 and 16:0) were oxidized as rapidly as pyruvate. Another six acids (16:1 n − 7, 18:0, 18:1 n − 9, 20:1 n − 9, 22:1 n − 9 and 22:6 n − 3) were oxidized at about three-quarters to one-half the rate of pyruvate. The two essential fatty acids (18:2 n − 6 and 18:3 n − 3) had a slow oxidation rate, about one-fifth of that of pyruvate. The liver mitochondria from rainbow trout oxidized 18:0, 18:1, 18:2, and 18:3 at the same rate, 70–80% of that of pyruvate. These results show that rainbow trout red muscle discriminates between fatty acids used in energy production and essential fatty acid precursors, as indicated by the low β-oxidation rate of the latter acids.