178 J. M. OLSON 



The spectrophotometric studies of Rhodo spirillum ruhrum and 

 Chromatium support the concept that a cytochrome system mediates 

 the overall reaction between "OH" and H2A shown in equation 3. 



Discussion 



Frenkel: I noticed that the reduction in the dark was relatively slow after the 

 light was turned off. I was wondering if the rate was appreciably different from 

 that in the Rhodospirillum which Dr. Chance talked about. 



Olson : Yes, it is appreciably different. In my illumination experiments, I often 

 had to wait as long as 10 minutes in order to be sure that the trace had returned 

 to the base line because of that very slow reduction. 



Frenkel : How long did Dr. Chance's experiment take? 



Chance : A matter of 30 seconds was adequate. 



Frenkel : Have you any explanation for that? 



Olson: I think that the cytochrome reductase system is perhaps weaker in 

 Chromatium than in Rhodospirillum. 



Linschitz : Was there any fast and slow phase in CO? 



Olson: I do not know, because I took only the dark steady-state difference 

 spectrum between reduced samples with and without CO. I observed no kinetics. 



Chance : It looks as if, when you turn the light on the CO-binding pigment, this 

 430-band is o.xidized and, in addition, some cytochrome c, indicated by the sharp 

 552-mM band. The bands that come in slowly are probably due to the remainder 

 of the cytochrome c and to cytochrome b. 



References 



1. Duysens, L. N. M., Nature, 173, 692 (1954). 



2. Chance, B., and Smith, L., Nature, 175, 803 fl955). 



3. Chance, B., Rev. Sci. Instr., 22, 634 (1951). 



4. Yang, C. C, and Legallais, V., Rev. Sci. Instr., 25, 801 (1954). 



5. Vernon, L. P., and Kamen, M. D., J. Biol. Chem., 211, 643 (1954). 



6. Van Niel, C. B., Advances in EnzymoL, 1, 324 (1941). 



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