Hysteretic behaviour of citrate synthase. Isotopically chiral citryl-CoA reveals increased number of reversals of the synthase condensation step under steady-state conditions.

Citrate specimens derived from chiral acetates were converted to the CoA derivatives. These were reconverted with citrate synthase to citrates under conditions of either predominating hydrolytic burst or predominating steady-state period. The stereochemical purity of substrates and products was determined. Reversal of the synthase condensation step occurs under both conditions but is markedly increased during the steady-state period. The results indicate that citryl-CoA-derived acetyl-CoA and oxaloacetate create the steady-state conditions. The hydrolase state and the ligase/lyase state of the synthase predominate under burst and steady-state conditions, respectively. This result indicates a conversion of the hydrolase state into the ligase/lyase state during the transition.