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 Mr-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 [14C]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 KD 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.
Ghadiminejad
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Department of Biochemistry, University College London, U.K.
Saggerson
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D000818:Animals; D015153:Blotting, Western; D002334:Carnitine O-Palmitoyltransferase / Q000737:chemistry*; D002352:Carrier Proteins / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism; D005215:Fasting; D007037:Hypothyroidism / Q000378:metabolism; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000201:enzymology; D007662:Ketosis / Q000378:metabolism; D008316:Malonyl Coenzyme A / Q000378:metabolism; D008930:Mitochondria, Liver / Q000201:enzymology* / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains
D002352:Carrier Proteins; D008316:Malonyl Coenzyme A; D002334:Carnitine O-Palmitoyltransferase