Two Different NADH Dehydrogenases in Respiration of Rhodospirillum rubrum Chromatophores

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Abstract
In Rhodospirillum rubrum chromatophores, oxidation of NADH by molecular oxygen was exhibited mostly by two different respiratory systems, one composed of NADH: hemeprotein oxidoreductase (enzyme-H), flavin, cytochrome B, and ubiquinone-10, and the other of NADH: quinone oxidoreductase (enzyme-Q) and flavin. These two systems were almost equal in their contribution to respiration. ATP formation was coupled with both systems. Added cytochrome c2 was reduced by the system involving enzyme-H, whereas 2,6-dichlorophenol indophenol (DCPI) was reduced by the system involving enzyme-Q. Since the rate of oxidation was depressed to half when the chromatophores were incubated either with antiserum against enzyme-H (antiserum-H) or with antiserum against enzyme-Q (antiserum-Q), it seems probable that the enzyme-H and enzyme-Q molecules were bound on the surface of the chro-matophore membrane in such a manner as to allow the antibodies to combine with their respective enzymes. The system involving enzyme-Q was able to reduce bound quinone at a relatively slow rate. In intact chromatophores, carbon monoxide did not combine with bound cytochrome B as well as bound cytochrome cc', although these hemeproteins were able to combine with carbon monoxide when the chromato-phore membrane was impaired. Conceivably, the main sites responsible for the reduction of molecular oxygen were the quinone in the system involving enzyme-H, and the flavin in the system involving enzyme-Q.

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