Nucleotide-depleted Beef Heart F1-ATPase Exhibits Strong Positive Catalytic Cooperativity

Catalytic cooperativity is a central feature of the binding change mechanism for F0F1-ATP synthases. However, in a recent publication (Reynafarje, B. D., and Pedersen, P. L. (1996) J. Biol. Chem. 271, 32546-32550), Reynafarje and Pedersen claim that cooperative effects are an artifact caused by endogenous nucleotides and that when such nucleotides are removed, the multiple catalytic sites on MF1 behave independently during ATP hydrolysis. In contrast to this conclusion, we show here that when ATP is loaded at a single catalytic site on nucleotide-depleted MF1, the rate of product release is accelerated by up to 5 x 10(4)-fold by the binding of ATP at adjacent catalytic sites. Hence, nucleotide-depleted MF1 is not an exception but does in fact show strong cooperative interactions. In addition, evidence is presented supporting a random order for product release during ATP hydrolysis.