The electron transport chain of Rhizobium trifolii.

The presence of a branched respiratory chain in Rhizobium trifolii grown in batch culture on a defined medium was demonstrated. The branches of the respiratory chain differ in sensitivity to inhibition by cyanide and in affinity for oxygen. The branching point is localized at cytochrome b-555. Electron flow from cytochrome b-555 via cytochrome c-549 and cytochrome a-597 towards oxygen has a relatively low affinity for oxygen and is sensitive to inhibition by cyanide. The second terminal oxidase is cytochrome b-561, which is directly linked to cytochrome b-555. This pathway has a higher affinity for oxygen. The pathway via cytochrome a-597 is more efficient in energy conservation than the pathway via cytochrome b-561, which lacks site III of oxidative phosphorylation.