Nested allosteric interactions in the cytoplasmic chaperonin containing TCP-1

Initial rates of ATP hydrolysis by the chaperonin containing TCP-1 (CCT) fr om bovine testis were measured as a function of ATP concentration. Two allo steric transitions are observed: one at relatively low concentrations of AT P (<100 <mu>M) and the second at higher concentrations of ATP. The data sug gest that CCT has positive intra-ring cooperativity and negative inter-ring cooperativity in ATP hydrolysis, with respect to ATP, as previously observ ed in the case of GroEL. It is shown that the relatively weak positive intr a-ring cooperativity found in the case of CCT may be due to heterogeneity i n its subunit composition. Our results suggest that nested allosteric behav ior may be common to chaperone double-ring systems.