Changes In Steady-state Levels Research Articles

Light-induced changes in ultraviolet absorption were investigated in a photosynthetic bacterium, Chromatium strain D. The difference spectra (light-minus-dark) of the changes in steady state level of absorption under various experimental conditions have common maxima (peaks or troughs) at 275 mμ, 315 mμ and 340 mμ; The sign of change, however, varied according to the conditions of illumination (see below). From the shape of the difference spectra and for other reasons discussed in the present paper, the changes at 275 mμ were ascribed to the oxidation-reduction changes of ubiquinone. Illumination under aerobic condition caused a reduction of ubiquinons amounting to about 6–7 percent of total ubiquinone in the cell. The addition of Na2S2O3 enhanced the amplitude of the photoinduced change to about 25% of the total ubiquinone in the cell. The sign of the photoinduced absorption change at 275 mμ was reverted by the presence of malate or succinate as substrate. On illumination under anaerobic condition, there was a photoinduced oxidation of ubiquinone amounting to about 50% of the total. Under aerobic condition the amount was about 6–7 percent of the total. Transitional changes of ubiquinone in the bacterial cell were also investigated under various experimental conditions.