The defective proton-ATPase of uncD mutants of Escherichia coli. Two mutations which affect the catalytic mechanism.

The catalytic characteristics of F1-ATPases from uncD412 and uncD484 mutant strains of Escherichia coli were studied in order to understand how these beta-subunit mutations cause defective catalysis. Both mutant enzymes showed reduced affinity for ATP at the first catalytic site. While uncD412 F1 was similar to normal in other aspects of single site catalysis, uncD484 F1 showed a Keq of bound reactants greatly biased toward bound substrate ATP and an abnormally fast rate of Pi release. Impairment of productive catalytic cooperativity was the major cause of the reduced steady state ("multisite") catalytic rate in both mutant enzymes. Addition of excess ATP to saturate second and/or third catalytic sites did promote ATP hydrolysis and product release at the first catalytic site of uncD412 F1, but the multisite turnover rate was significantly slower than normal. In contrast, with uncD484 F1, addition of excess ATP induced rapid release of ATP from the first catalytic site and so productive catalytic cooperativity was almost completely absent. The results show that both mutations affect properties of the catalytic site and catalytic site cooperativity and further that the relatively more severe uncD484 mutation affects a residue which acts as a determinant of the fate of bound substrate ATP during promotion of catalysis. Taken together with previous studies of uncA mutant F1-ATPases (Wise, J. G., Latchney, L. R., Ferguson, A. M., and Senior, A. E. (1984) Biochemistry 23, 1426-1432) the results indicate that catalytic site cooperativity in F1-ATPases involves concerted beta-alpha-beta intersubunit communication between catalytic sites on the beta-subunits.