Coupling of "high-energy" phosphate bonds to energy transductions.

Recent results suggest consideration of a new concept for oxidative phosphorylation in which a prime function of energy is to bring about release of ATP formed at the catalytic site by reversal of hydrolysis. Data with submitochondrial particles include properties of an uncoupler insensitive Pi=HOH exchange, a rapid reversible formation of bound ATP in presence of uncouplers, and predictable patterns of 32-Pi incorporation into ATP in rapid mixing experiments. ADP is confirmed as the primary Pi acceptor in mitochondrial ATP synthesis, but with chloroplasts ADP is also rapidly labeled. Other findings with pyrophosphatase and with transport ATPase harmonize with the new concept. Measurements of the reversal of ATP cleavage and binding by myosin suggest that oxygen exchanges result from reversible cleavage of ATP to ADP and Pi at the catalytic site and that the principal free energy change in ATP cleavage occurs in ATP binding. Reversal of conformational changes accompanying ATP binding and cleavage is proposed to drive the actin filament in contraction. Thus energy transductions linked to ATP in both mitochondria and muscle may occur primarily through protein conformational change.