A bi-site mechanism for Escherichia coli F1-ATPase accounts for the observed positive catalytic cooperativity

Nucleotide binding to nucleotide-depleted F1-ATPase from Escherichia coli (EcF1) during MgATP hydrolysis in the presence of excess ɛ subunit has been studied using a combination of centrifugal filtration and column-centrifugation methods. The results show that nucleotide-binding properties of catalytic sites on EcF1 are affected by the state of occupancy of noncatalytic sites. The ATP-concentration dependence of catalytic-site occupancy during MgATP hydrolysis demonstrates that a bi-site mechanism is responsible for the positive catalytic cooperativity observed during multi-site catalysis by EcF1. The results suggest that a bi-site mechanism is a general feature of F1 catalysis.