| Abstract: | Mitochondria isolated from the livers of sheep and rats were shown to oxidize palmitate, oleate and linoleate in a tightly coupled manner, by monitoring the oxygen consumption associated with the degradation of these acids in the presence of 2mM-L-malate. Rat liver mitochondria oxidized linoleate and oleate at a rate 1.2-1.8 times that of palmitate. Sheep liver mitochondria had a specific activity for the oxidation of palmitate that was 50-80% of that of rats and a specific activity for the oxidation of oleate and linoleate that was 30-40% that of rats. This would indicate that sheep conserved linoleate by limiting its oxidation. Carnitine acyltransferase I (CAT I) actively esterified palmitoyl-CoA and linoleate to carnitine in both rat and sheep liver mitochondria, and in both cases the rate for linoleate was faster than for palmitate. The CAT I reaction in both rat and sheep liver was inhibited by micromolar amounts of malonyl-CoA. With 90 microM-palmitoyl-CoA as substrate, CAT I was inhibited by 50% with 2.5 microM-malonyl-CoA in rats, and in sheep, 50% inhibition was found with all malonyl-CoA concentrations tested (1-5 microM). With 90 microM-linoleate as substrate for CAT I, a much larger difference in response to malonyl-CoA was seen, the rat enzyme being 50% inhibited at 22 microM-malonyl-CoA, whereas sheep liver CAT I was 91% and 98% inhibited at 1 microM- and 5 microM-malonyl-CoA respectively. We propose that malonyl-CoA may act as an important regulator of beta-oxidation in sheep, discriminating against the use of linoleate as an energy-yielding substrate. |
