THE ELECTRON-TRANSPORT SYSTEM OF THE HALOPHILIC PURPLE NONSULFUR BACTERIUM RHODOSPIRILLUM-SALINARUM .1. A FUNCTIONAL AND THERMODYNAMIC ANALYSIS OF THE RESPIRATORY-CHAIN IN AEROBICALLY AND PHOTOSYNTHETICALLY GROWN CELLS

Plasma membranes isolated from cells of the halophilic purple nonsulfu r bacterium Rhodospirillum salinarum grown in light or in the dark wer e examined. Membranes isolated from cells grown aerobically in the dar k contained three b-type and two c-type membrane-bound cytochromes wit h E-m.7 of +180, +72 and -5 mV (561-575 nm), and +244 and +27 mV (551- 540 nm), respectively. Conversely, membranes isolated from cells grown anaerobically in the light contained two 6-type and five c-type haems with E-m.7 of +60 and -45 mV and +390, +250, +135, -20 and -105 mV, r espectively, In addition to haems of the b- and c-type, two haems of t he a-type (E-m.7 of +325 and +175 mV) were present only in cells grown in the dark. Four soluble cytochromes of the c type, but not cytochro me c(2), along with two high-potential iron-sulfur proteins (HiPIP iso -1 and iso-2) were also identified in cells grown aerobically. Inhibit ory studies showed that 85-90% of the respiratory activity was blocked by very low concentrations of cyanide, antimycin A and myxothiazol (5 0, 0.1 and 0.2 mM, respectively). These results taken together were in terpreted to show that the oxidative electron transport chain of Rsp. salinarum urn is linear, leading to a membrane-bound oxidase of the aa (3) type in cells grown in the dark, while no significant cytochrome o xidase activity is catalyzed by photosynthetic membranes, These featur es suggest that this halophilic species is unique among the genus Rhod ospirillum and that it also differs from other facultative phototrophs (e.g., Rhodobacter species) in that it does not contain either cytoch rome c(2) or a branched respiratory chain.