Recovery of the alternative oxidase dependent electron flow by fusion of membrane vesicles from Rhodobacter capsulatus mutant strains

Membranes from the facultative photosynthetic bacterium Rhodobacter capsulatus can be fused by sonication in vitro to form hybrid membranes, some of which are vesicles. The organization of the redox complexes involved in alternative-oxidase dependent electron transport of R. capsulatus can be studied by testing for in vitro complementation of this activity lacking in membranes from genetic mutants. The results obtained in complementation tests between well characterized mutants support current models of organization of electron transport components in R. capsulatus and confirm the in situ existence of independent functional entities such as NADH-dehydrogenase, reaction center, bacteriochlorophyll light-harvesting complexes and alternative-oxidase (cyt. o). The demonstration that artefactual mixing between different membrane entities may only be induced by treatments such as ultrasonic irradiation promoting intervesicular recombination has been taken as evidence that photorespiratory processes truly reflect an in vivo situation.