KINETIC INVESTIGATION OF COOPERATIVITY IN COENZYME BINDING BY TRANSKETOLASE ACTIVE-SITES

The two-step mechanism of coenzyme (thiamine diphosphate, ThDP) bindin g with two initially identical active sites of apotransketolase has be en examined with a kinetic model. Cooperativity between sites in the p rimary ThDP binding and in the following conformational transition has been analyzed. The only reliable difference between sites is shown to be the tenfold difference in the backward rate constants of the confo rmational transition; this means that the cooperative interaction betw een sites takes place only after termination of both steps of ThDP bin ding in both sites.