A STUDY OF PROPERTIES AND ABUNDANCE OF THE COMPONENTS OF LIVER CARNITINE PALMITOYLTRANSFERASES IN MITOCHONDRIAL INNER AND OUTER MEMBRANES - EFFECTS OF HYPOTHYROIDISM, FASTING AND A KETOTIC DIABETIC STATE

1. Liver mitochondrial outer and inner membranes were isolated from normal, 48 h-fasted, streptozotocin-diabetic and hypothyroid rats. 2. Relative to membrane protein, fasting and diabetes substantially increased the activity of carnitine palmitoyltransferase (CPT) in outer membranes. Inner-membrane CPT specific activity was only slightly altered, being increased in diabetes and decreased in hypothyroidism. Abundance of an inner-membrane M(r)-68 000 polypeptide that cross-reacted with an anti-CPT serum was significantly increased in diabetes and hypothyroidism. Relative to inner-membrane CPT activity, this cross-reactivity was increased by 37 % in diabetes and by 400 % in hypothyroidism, suggesting modification of the intrinsic activity of the CPT in these states. 3. CPT in outer membranes was inhibitable by malonyl-CoA, whereas inner-membrane CPT was insensitive to malonyl-CoA. Fasting and diabetes increased the IC50 (concentration of malonyl-CoA causing 50 % inhibition) for outer-membrane CPT, whereas the IC50 was decreased in hypothyroidism. 4. Binding of [C-14]malonyl-CoA was observed with both outer and inner membranes and was fitted to two-site models in each case. Fasting, diabetes and hypothyroidism changed the K(D) for binding at the higher-affinity site in outer membranes in a manner that correlated closely with changes in IC50 for inhibition of outer-membrane CPT by malonyl-CoA. Fasting and diabetes increased the abundance of this outer-membrane high-affinity malonyl-CoA-binding site, whereas hypothyroidism decreased its abundance.