Initial rate kinetic studies of succinyl coenzyme A synthetase of E. coli in the direction of succinyl-CoA cleavage are consistent with the operation of a partially random sequential kinetic mechanism with initial binding of ADP followed by random association of succinyl-CoA and Pi. The mechanism is analogous to that proposed previously for the succinyl-CoA formation reaction, and thus the kinetic mechanism of the overall reversible succinyl-CoA synthetase reaction appears to be symmetrical.Studies of the kinetics of [Formula: see text] isotope exchange at equilibrium show that this partially random sequential kinetic mechanism is not an exclusive pathway. [Formula: see text] isotope exchange rates did not show complete substrate inhibition when CoA or succinate was varied in constant ratio with Pi. However, when CoA or succinate was varied in constant ratio with succinyl-CoA, nearly complete substrate inhibition was observed. These results can be interpreted in terms of a wide variety of minor pathways of substrate binding and product release available to the enzyme under various conditions.
Succinyl-Coenzyme A Synthetase and its Role in δ-Aminolevulinic Acid Biosynthesis in Euglena gracilis
