Preferential interaction parameters for F 1-ATPase from a thermophilic bacterium (PS3)

Abstract

The proton translocating ATPase of energy transducing membranes couples the vectorial transport of protons through the membrane to synthesize ATP. The enzyme can be divided into an integral membrane portion, F,, and a peripheral portion, called the coupling factor or Fr-ATPase, which contains the catalytic site of ATP synthesis and hydrolysis [l-3]. The Fr portion of the H’-ATPase consists of 5 different subunit species, OL,/~,T,~ and E. The subunits have been isolated of Fr from Escherichia coli, PS3 and CFr [4-61, and their amino acid composition and Mr-values determined [7]. The subunit stoichiometry is still controversial because of incomplete reassembly to a functional Fr of the isolated subunits [7]. Also, the reported J&-values of Fr vary from 350 OOO380 000, e.g., for ECFr [9,10], due to differences in analytical methods and preparations. However, analytical ultracentrifugation data were not treated as a multicomponent system with c2 the mass of the protein (Fr), c3 the added solvent component, e.g., methanol or glycerol, and cr the principal solvent (buffer) with cr in g/ml solution. This paper reports on studies of TFr in 0.01 M Tris-HCI buffer at pH 7.0-8-O in the presence and absence of methanol and glycerol by means of light scattering and differential refractometry experiments, in order to detect any interactions of component three with the protein. Since these organic solvents