Abstract
1. 1. ATP dependent acyl-CoA synthetase is localized mainly in the outer mitochondrial membrane fraction with a small activity present in the inner membranematrix fraction. The specific activity of the enzyme present in the outer membrane is much greater than that present in the inner membrane, approx. 26:1 after correcting for microsomal and outer membrane contamination in the inner membrane fraction. The synthetase in the outer membrane fraction is easily removed from the membrane by treatment of the mitochondria with digitonin and subsequent centrifugation. Treatment with digitonin also causes a 40% loss in total enzymic activity in the mitochondria. 2. 2. GTP dependent acyl-CoA synthetase is absent from the outer membrane of the mitochondria and is exclusively associated with the inner membrane-matrix fraction. The enzyme appears to be equally associated with the matrix and membranous residue of the inner membrane-matrix fraction. The specific activity of the GTP dependent enzyme of the inner membrane-matrix fraction is approx. 4.0% of the specific activity of the ATP dependent enzyme present in the outer membrane. 3. 3. Based on the rates of acyl-CoA formation from palmitate, it is suggested that activation of long chain fatty acids is not the rate limiting step in β-oxidation, chain elongation or incorporation of acyl-CoA compounds into phospholipids in the mitochondria.
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