Respiration-linked proton translocation in the moderate thermophileBacillus stearothermophilus

Abstract

The majority of bacterial respiratory chains which have so far been investigated exhibit ---> H + / O quotients which do not exceed 8 g-ion H +/g-atom O for the oxidation of endogenous substrates or internal NADPH. This value decreases to approximately 6 in organisms which lack an, active, energy-linked nicotinamide nucleotide transhydrogenase or which do not synthesise, or use, a high redox potential cytochrome c, and does not exceed 4 when both of these components are functionally absent [1-4]. The absence of cytochrome c, but not transhydrogenase, also significantly decreases the efficiency of growth [3,4]. These results have generally been interpreted as indicating the presence in the respiratory chain of up to four energy coupling sites, viz. at the level of transhydrogenase (site 0), NADH dehydrogenase (site 1), and the quinone-cytochrome-cytochrome