SIGMOID KINETICS OF PURIFIED BEEF-HEART MITOCHONDRIAL CARNITINE PALMITOYLTRANSFERASE - EFFECT OF PH AND MALONYL-COA

  • 1 January 1984
    • journal article
    • research article
    • Vol. 259  (21) , 3084-3088
Abstract
The kinetics of purified beef heart mitochondrial carnitine palmitoyltransferase were extensively investigated with a semiautomated system and the computer program TANKIN, and shown to be sigmoidal with both acyl-CoA and L-carnitine. In contrast, Michaelis-Menten kinetics were found with carnitine octanoyltransferase. The catalytic activity of carnitine palmitoyltransferase is strongly pH dependent. The K0.5 and Vmax are both greater at lower pH. The K0.5 for palmitoyl-CoA is 1.9 and 24.2 .mu.M at pH 8 and 6, respectively. The K0.5 for L-carnitine is 0.2 and 2.9 mM at pH 8 and 6, respectively. Malonyl-CoA (20-600 .mu.M) had no effect on the kinetic parameters for palmitoyl-CoA at both saturating and subsaturating levels of L-carnitine. Nalonyl-CoA is not a competitive inhibitor of carnitine palmitoyltransferase. The purified enzyme contained 18.9 mol of bound phospholipid/mol of enzyme which were identified as cardiolipin, phosphatidylethanolamine and phosphatidylcholine by TLC. Native carnitine palmitoyltransferase exhibits different catalytic properties on either side of the inner membrane of mitochondria due to its non-Michaelis-Menten kinetic behavior, which can be affected by pH differences and differences in membrane environment.