The Effect of Hydrosulfite on the Anaerobic 



Light Effect 



BRITTON CHANCE and LUCILE SMITH, Johnson Foundation for 

 Medical Physics, University of Pennsylvania, Philadelphia, Pennsylvania 



In the course of our studies of the effect of infrared illumination 

 upon the steady-state oxidation-reduction levels of the cytochromes 

 of R. rubrum, we have attempted to determine whether the oxida- 

 tion of cytochromes is prevented by the well-known reducing agent, 

 sodium hydrosulfite (1). 



A typical experiment is sho^ai in Fig. 1. The tracings were made 

 in the double-beam spectrophotometer by recording the differences of 

 optical density at 430 as compared with 440 ni/z. In the left-hand 

 trace, the aerobic cells exhaust the oxygen dissolved in the solution 

 and become anaerobic. This causes reduction of the hemoprotein ab- 

 sorbing at 430 m/i, as is indicated by the downward sweep of the 

 trace. Illumination with infrared light causes partial oxidation of 

 this pigment and darkness leads to a restoration of the reduced state. 



This suspension is then shaken vigorously in order to aerate it and is 

 then replaced in the spectrophotometer. Proof of adequate aeration is 

 afforded by the identical levels of optical density in the initial por- 

 tions of the two records. Addition of sohd sodium hydrosulfite to give 

 a final concentration of roughly 1 mM now causes a rapid reduction 

 that proceeds considerably farther than in the first recording. When 

 the trace has reached an end point, the light is turned on, and again 

 an oxidation of the hemoprotein is obtained. Quantitatively, the 

 optical density change on reduction is 18% greater in the presence of 

 hydrosulfite, while the optical density change on infrared illumina- 

 tion increases 5%. In order to show that an excess of hydrosulfite is 

 present, we made a second addition of hydrosulfite to such a solution 

 and still obtained the oxidation reaction upon illumination. At higher 

 hydrosulfite levels the light effect is diminished. Other evidence in 

 favor of an excess of hydrosulfite is based on the fact that the addition 

 of a low concentration of ox3^gen l)y stirring the solution caused no 

 transient oxidation of the cytochromes. 



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