CATALYTIC PROPERTIES OF ESCHERICHIA-COLI F1-ATPASE DEPLETED OF ENDOGENOUS NUCLEOTIDES

Nucleotide-depleted Escherichia coli F1 was prepared by the procedure of Wise et al. (1983, Biochem. J. 215, 343-350). This enzyme had high rates of steady-state ATPase and GTPase activity. When "unisite" ATP hydrolysis was measured using an F1 ATP concentration ratio of 10, all of the substoichiometric ATP became bound to the high-affinity catalytic site and none became bound to noncatalytic sites. The association rate constant for ATP binding was 7 × 105 m-1 s-1 and the KdATP was 7.9 × 10-10 m, as compared to values of 3.8 × 105 m-1 s-1 and 1.9 × 10-10 m, respectively, in native (i.e., nucleotide-replete) F1. Rate constants for bound ATP hydrolysis, ATP resynthesis, and Pi release, and the reaction equilibrium constant, were similar in nucleotide-depleted and native F1. Therefore, we conclude that occupancy of the noncatalytic sites is not required for formation of the high-affinity catalytic site of F1 and has no significant effect on unisite catalysis. In further experiments we looked for the occurrence of inhibitory, catalytic-site-bound MgADP in E. coli F1. Such an entity has been reported for chloroplast and mitochondrial F1. However, our experiments gave no indication for inhibitory MgADP in E. coli f1. © 1992.