An increase in the ionic strength of the assay medium markedly increased the basal activity of the malonyl-CoA-sensitive carnitine medium/long chain acyltransferases in peroxisomes and microsomes and decreased the malonyl-CoA inhibition. 2. ATP-Mg largely reversed the salt mediated stimulation of both the peroxisomal and the microsomal activities. 3. The octylglucoside solubilization of the peroxisomes and microsomes caused only marginal losses of their catalytic activity but the malonyl-CoA inhibition was nearly fully abolished. 4. Starvation increased the above activity of peroxisomes and microsomes and decreased their sensitivity to malonyl-CoA inhibition. Tritiated etomoxir labeled a approximately 47 kDa peptide in these organelles, the intensity of which was decreased on starvation. Collectively these findings strengthen the notion that the malonyl-CoA sensitive carnitine acyltransferases in mitochondria, microsomes, and peroxisomes are distinct proteins.
