The interaction of the free radical of 5-methylphenazinium methyl sulfate with the light-induced free radical of Rhodospirillum rubrum chromatophores.

In an earlier communication we reported certain effects which 5-methylphenazinium methyl sulfate (P1MtS) had on the decay of light-induced absorbancy and electron spin resonance signals of bacterial chromatophores.' At this time, we are reporting on additional observations relating to the interaction of PM\1S with light-induced spectral changes. The most striking phenomenon which we have observed appears to be a radicalradical interaction of the free radical produced when chromatophores are illuminated2' I with the free radical N-methylphenazinium (PM ). When P1\/MS is incubated with chromatophores, PMVIS appears in total darkness and in the absence of any exogenous electron donors. Upon illumination of such a preparation with red light, PM interacts with the chromatophore free radical in a manner which will be discussed below. Radical-radical interactions have been studied extensively in nonbiological systems,4' 5 and a report on the interaction of N,N,N', N'-tetramethyl-p-phenylenediamine dihydrochloride (TM/IPD) with chromatophores has been presented.6 Materials and Methods.-Washed chromatophores were prepared as reported previously.7 ESR determinations were carried out on a modified Varian 100-kc spectrometer equipped with a Fieldial controlled 12-inch magnet. Spin concentrations were measured in a double cavity, with a standardized pitch sample as the reference, by integrating the first moments. Spectrophotometric determinations were done with a Cary model 14. The details for the experimental procedures were reported elsewhere.' All measurements were carried out at light saturation, which was approximately 1 X 10 erg cm-2 -sec1. Illumination was through a Corning CS7-69 deep-red filter. PMS' was prepared by following the initial steps for the preparation of fully reduced PMS as presented by Zaugg.8 The bluegreen precipitate was stable when stored in benzene at 0?C for at least five months. P'rior to taking a spectrum, the precipitate was extracted from the benzene with 0.2NHCI. Results.-Previous investigators have reported that illumination of chromatophores produces an ESR signal with a line width of about 10 gauss and a g value of 2.002.9 This ESR spectrum is shown in Figure 1 (insert a); we have obtained a g value of 2.0023 i 0.0002. The spectrum obtained when PMVIS is incubated with chromatophores is seen in Figure 1 (insert b) and in greater detail in Figure 2b. This spectrum lacks the hyperfine structure present in the chemically prepared material though both exhibit the same g values within experimental error (g = 2.0034 i 0.0002 for PMS' in chromatophores and 2.0031 i 0.0002 for the chemically produced PM\1S ). It was