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Regulation of Bacteriochlorophyll Synthesis by Oxygen in Respiratory Mutants of Rhodopseudomonas capsulata

^a Department of Microbiology, Indiana University, Bloomington, Indiana 47401

ABSTRACT

Respiratory mutants of the facultative photosynthetic bacterium Rhodopseudomonas capsulata were used to investigate the mechanism of (reversible) inhibition of bacteriochlorophyll (BChl) synthesis by molecular oxygen. Although mutant strain M5 lacks cytochrome oxidase activity, it closely resembles the parental wild-type strain in respect to the effect of O₂ on BChl formation. This observation does not support an earlier hypothesis that O₂ regulates BChl synthesis through an effect on the redox state of a component of the respiratory electron transport system. Mutant strain M2 shows normal cytochrome oxidase activity, but lacks both reduced nicotinamide adenine dinucleotide and succinate dehydrogenase activities; relative to the parental strain, BChl synthesis in M2 is more sensitive to O₂ inhibition. The foregoing and results of related experiments can be accounted for by a revised interpretation of the O₂ effect, which proposes that O₂ directly inactivates a "factor" necessary for BChl formation and that, at relatively low O₂ tension, the inactivation can be reversed by a flow of electrons (derived from reduced nicotinamide adenine dinucleotide and succinate) diverted from a portion of the electron transport system delimited by the mutational blocks in M2 and M5.

¹ Present address: Department of Biochemistry, St. Louis University School of Medicine, St. Louis, Mo. 63104.

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