Fatty acid metabolism in skeletal muscle mitochondria from two strains of dystrophic mice

Several aspects of fatty acid metabolism have been examined in skeletal muscle mitochondria from both strain 129 dystrophic (dy/dy) and myodystrophic (myd/myd) mice. Skeletal muscle mitochondria from dy/dy mice showed significantly decreased state 3 respiratory rates with both palmityl- and acetyl-carnitine + malate as substrates when compared with their normal littermate controls. A similar, though less severe impairment in acylcarnitine oxidation by mitochondria from myd/myd skeletal muscle has also been shown by us in a previous study. In the present study, kinetic measurements revealed decreased activities of the reverse carnitine palmityltransferase (palmitylcarnitine + CoASH as substrates) in intact mitochondria from dy/dy muscle, and of citrate synthase in myd/myd muscle mitochondria. However, neither of these reactions appeared to be rate limiting for acylcarnitine oxidation in mouse skeletal muscle mitochondria. All other enzyme activities or cofactor contents measured were either comparable to those of controls or were higher. The results reported here indicate that neither of the impairments in acylcarnitine oxidation by skeletal muscle mitochondria from dy/dy or myd/myd mice is due to deficiencies in either carnitine palmityltransferase, carnitine acetyltransferase, citrate synthase, coenzyme A, or substrate-reducible flavoprotein.