Active sites residues of beef liver carnitine octanoyltransferase (COT) and carnitine palmitoyltransferase (CPT-II) Available to Purchase

The carnitine acyltransferases which catalyse the reversible transfer of fatty acyl groups between carnitine and coenzyme A have been proposed to contain a catalytic histidine. Here, the chemical reactivity of active site groups has been used to demonstrate differences between the active sites of beef liver carnitine octanoyltransferase (COT) and carnitine palmitoyltransferase-II (CPT-II). Treatment of CPT-II with the histidine-selective reagent, diethyl pyrocarbonate (DEPC), resulted in simple linear pseudo-first-order kinetics. The reversal of the inhibition by hydroxylamine and the pK_a (7.1) of the modified residue indicated that the residue was a histidine. The order of the inactivation kinetics showed that 1 mol of histidine was modified per mol of CPT-II.