Abstract
Suspensions of chromatophores from the blue-green mutant (G-9) of Rhodospirillum rubrum were illuminated by 592-nm actinic light, and the consequent steady-state absorbance changes in the near infra-red region were studied:
1) In chromatophores, there are two different types of pigments which undergo light-induced absorbance changes in the spectral region. The two pigments are called Liac-860 and Liac-890 in this paper.
2) Liac-860 is a major pigment responsible for the negative peaks (photo-bleaching) at 860nm and 810nm and the positive peak (photo-coloring) at 790nm in the light-minus-dark difference spectrum, whereas Liac-890 is a pigment responsible for the positive peak at 890nm in the spectrum. The midpoint oxidation-reduction potentials for these changes of Liac-860 and Liac-890 are +0.45 volt (n=1) and a value more negative than -0.1 volt, respectively.
3) These absorbance changes of Liac-860 and Liac-890 are influenced by the inhibitors of the electron transport system (antimycin A, 2-n-heptyl-4-hydroquinoline-N-oxide and phenylmercuric acetate), by the energy-trapping system (ADP plus P_??_), and by the uncouplers (2, 4-dinitrophenol, atabrine dihydrochloride, carbonyl cyanide m-chlo-rophenylhydrazone and ADP plus arsenate), but not by the inhibitor of the energy conservation system (oligomycin).
4) The absorbance changes of Liac-860 and Liac-890 are influenced by proton concentration in the absence of antimycin A, but not in its presence.
5) It is discussed that the light-induced absorbance changes take place on the conversion of Liac-860 to Liac-860+ and of Liac-890 to Liac-890-: Liac-860+ and Liac-890-are the primary electron acceptor and donor, respectively, for the electron transport system which involves a step influenced by proton concentration.
