Fo∙F1 ATP-synthase/ATPase of Paracoccus denitrificans: Mystery of Unidirectional Catalysis

Abstract

F_o∙F₁ ATP synthases/ATPases (F_o∙F₁) catalyze ATP synthesis by consuming energy of electrochemical potential of hydrogen ions (pmf), or ATP hydrolysis resulting in the pmf formation. It is generally accepted to consider F_o∙F₁ as a reversible chemomechanical-electrical molecular machine, however: (i) the mechanism of energy-dependent ATP synthesis is based only on the data on hydrolytic activity of the enzyme, (ii) F_o∙F₁ from a number of organisms effectively synthesize, but is unable to hydrolyze ATP, which indicates non-observance of the principle of microreversibility and requires development of a new hypotheses concerning the enzyme mechanism. Since 1980, the group of A. D. Vinogradov has been developing a concept according to which the elementary catalysis stages of ATP hydrolysis and ATP synthesis do not coincide, and there are two independently operating forms of F_o∙F₁ in the coupled membranes – pmf-generating ATPase and pmf-consuming ATP synthase. F_o∙F₁ of P. denitrificans as a natural model of an irreversibly functioning enzyme is a convenient object for experimental verification of the hypothesis of unidirectional energy conversion. The review considers modern concepts of the molecular mechanisms of regulation of F_o∙F₁ ATP synthase/ATPase of P. denitrificans and development of the hypothesis of two forms of F_o∙F₁.