Two different NADH dehydrogenases in respiration of Rhodospirillum rubrum chromatophores.

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.