Different sites of inhibition of carnitine palmitoyltransferase by malonyl-CoA, and by acetyl-CoA and CoA, in human skeletal muscle.
The inhibition of carnitine palmitoyltransferase (CPT, EC 2.3.1.21) by malonyl-CoA, acetyl-CoA and free CoA was studied in sonicated skeletal-muscle homogenates from normal human subjects and from five patients with a mutant CPT [Zierz & Engel (1985) Eur. J. Biochem. 149, 207-214]. (1) Malonyl-CoA, acetyl-CoA and CoA were competitive inhibitors of CPT with palmitoyl-CoA. (2) Acetyl-CoA and CoA inhibited normal and mutant CPT to the same degree, whereas malonyl-CoA inhibited mutant CPT more than normal CPT. (3) Triton X-100 abolished the inhibition of normal CPT by malonyl-CoA, but not by acetyl-CoA or CoA. Triton X-100 by itself caused loss of activity of the mutant CPT. (4) In the concentration range 0.1-0.4 mM, the inhibitory effects of any two of the three inhibitors were synergistic. (5) The inhibitory constants (Ki) for acetyl-CoA and CoA were close to 45 microM. The Ki for malonyl-CoA was 200-fold lower, or 0.22 microM. Addition of 40 microM-acetyl-CoA or CoA resulted in a 3-fold increase in the Ki for acetyl-CoA. Addition of 20 microM-CoA resulted in a 3-fold increase in the Ki for acetyl-CoA. (6) The findings indicate that acetyl-CoA and CoA can inhibit CPT at the catalytic site or a nearby site which is different from that at which malonyl-CoA inhibits CPT. (7) The fact that small changes in the concentration of acetyl-CoA and CoA can antagonize the inhibitory effect of malonyl-CoA suggests that these compounds could modulate the inhibition of CPT by malonyl-CoA.
Zierz
S
S
Department of Neurology, Mayo Clinic, Rochester, MN 55905.
Engel
A G
AG
D000105:Acetyl Coenzyme A / Q000494:pharmacology*; D000214:Acyl Coenzyme A / Q000494:pharmacology*; D000217:Acyltransferases / Q000037:antagonists & inhibitors*; D001665:Binding Sites; D002334:Carnitine O-Palmitoyltransferase / Q000037:antagonists & inhibitors*; D003065:Coenzyme A / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D008316:Malonyl Coenzyme A / Q000494:pharmacology*; D009132:Muscles / Q000201:enzymology*; D017830:Octoxynol; D011092:Polyethylene Glycols / Q000494:pharmacology
D000214:Acyl Coenzyme A; D011092:Polyethylene Glycols; D008316:Malonyl Coenzyme A; D000105:Acetyl Coenzyme A; D017830:Octoxynol; D000217:Acyltransferases; D002334:Carnitine O-Palmitoyltransferase; D003065:Coenzyme A