Studies of medium-chain fatty acyl-coenzyme A synthetase. Enzyme fraction II: mechanism of reaction and specific properties

1. The mechanism of reaction of fatty acyl-CoA synthesis catalysed by fatty acyl-CoA synthetase from ox liver (fraction II; Bar-Tana, Rose & Shapiro, 1968) was investigated by a kinetic study of CoA disappearance dependent on butyrate plus ATP or butyryl-AMP (overall and partial reaction b respectively). 2. Contrary to findings with another enzyme (fraction I), a Bi Uni Uni Bi Ping Pong mechanism (Cleland, 1963a,b,c) corresponding to Berg's (1956) scheme of reaction was eliminated and an ordered Ter Ter mechanism with an A–C–B (standing for ATP, CoA and butyrate respectively) sequence of substrate entry for the overall reaction was established for fraction II. Partial reaction (b) was found to follow the ‘Iso-Theorell–Chance’ mechanism. 3. Also, in contrast with results obtained with fraction I, no allosteric properties could be demonstrated with fraction II.