Interaction of short-chain and branched-chain fatty acids and their carnitine and CoA esters and of various metabolites and agents with branched-chain 2-oxo acid oxidation in rat muscle and liver mitochondria

Abstract

1. 1. Interaction of various compounds with the 14CO 2 production from [1- 14C]-labelled branched-chain 2-oxo acids was studied in intact rat quadriceps muscle and liver mitochrondria. 2. 2. In the absence of carnitine, CoA esters of short-chain and branched-chain fatty acids, CoA and acetyl- l-carnitine stimulated oxidation of 4-methyl-2-oxopentanoate and 3-methyl-2-oxobutanoatee in muscle mitochondria. Octanoyl- l-carnitine inhibited oxidation of the latter, but stimulated that of the former substrate. Isovaleryl- l-carnitine was inhibitory with both substrates. 3. 3. Carnitine stimulates markedly 3-methyl-2-oxobutanoate oxidation in liver mitochondria at substrate concentrations higher than 0.1 mM, in contrast to 4-methyl-2-oxopentanoate oxidation. 4. 4. In the presence of carnitine, 3-methyl-2-oxobutanoate oxidation was inhibited in muscle and liver mitochondria by octanoate, octanoyl- l-carnitine and isovaleryl- l-carnitine. The latter ester and octanoyl- d-carnitine inhibited also 4-methyl-2-oxopentanoate oxidation in muscle mitochondria. 5. 5. Branched-chain 2-oxo acids inhibited mutaly their oxidation, except that 3-methyl-2-oxobutanoate did not inhibit 4-methyl-2-oxopentanoate oxidation in liver mitochondria. Their degradation products, isovalerate, 3-methylcrotonate, isobutyrate and 3-hydroxyisobutyrate inhibited to a different extent 2-oxo acid oxidation in liver mitochondria. 6. 6. The effect of CoA esters was studied in permeabilized and with cofactors reinforced mitochondria. Acetyl-CoA and isovaleryl-CoA inhibited only 3-methyl-2-oxobutanoate oxidation in muscle mitochondria. Octanoyl-CoA inhibited oxidation of both 2-oxo acids in muscle and 4-methyl-2-oxopentanoate oxidation in liver mitochondria. 7. 7. Pyruvate and ketone bodies decreased only 3-methyl-2-oxobutanoate oxidation in liver mitochondria. 2-Chloro-4-methyl-2-oxopentanoate and dichlorocetate inhibited oxidation in liver, but stimulated it in muscle mitochondria. Clofibric acid, 2-cyanocinnamate, mersalyl and sulfobetaine caused a marked inhibition in all cases, tetradecylglycidic acid and amino-oxyacetate had only an inhibitory effect in muscle mitochondria. 8. 8. Results were discussed in relation to the previously observed interactions in intact muscle and the further degradation pathway and/or mitochondrial export of the formed branched-chain acyl groups.