Abstract
The intensity dependences of light-induced reactions in Chromatium have been determined spectrophotometrically. The intensities of near-infrared irradiation required for half-maximum oxidation of the various cytochrome species are in the proportion 1:500:~4000 for C 423.5, C 426, and the combination of C 422 and C 430. The quantum requirement for intracellular cytochrome 423.5 oxidation has been determined by measuring the initial rate of absorbancy change (423 mμ) in anaerobic bacteria upon irradiation with monochromatic yellow light (589 mμ) of known quantum intensity. This requirement is 2 quanta per electron at both 11 and 29 °C. A hypothetical structure for the cytochrome system in Chromatium consists of three distinct electron-transfer pathways. The pathway including C 423.5 is of primary importance in photosynthesis.
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