NONHEME IRON PROTEINS 



323 



350 400 450 500 



WAVELENGTH (mp) 



550 



600 



Fig. 4. Difference spectrum (photooxidized-minus-reduced) of Chroma- 

 tium iron protein. The reaction conditions described under Fig. 3 were 

 used except that reduced iron protein was included in both reference and 

 sample cuvettes. 



cytochrome which can be readily reduced by an oxidation- reduction 

 agent with as positive a potential as that of the iron protein ( Ej^, 

 pH 7 = +0.35 volt). 



In experiments to be published elsewhere, performed with Dr. J. 

 M. Olson, rapid and reversible photooxidation of the cytochromes of 

 Chromatmm chromatophores supplemented with reduced iron protein 

 was observed. The light- minus- dark difference spectrum obtained with 

 a double beam spectrophotometer resembled spectra of light-induced 

 changes in whole cells of Chromatium reported by Olson and Chance 

 (22). 



DISCUSSION 



The evidence presented here seems to implicate Chromatium iron 

 protein as a component of the chromatophore electron transfer sys- 

 tem in an as yet unknown role. The iron protein can be isolated from 

 chromatophores together with cytochromes which are believed to 

 participate in light-induced reactions in the chromatophore. Added iron 

 protein undergoes a reversible anaerobic photooxidation in the pres- 

 ence of illuminated chromatophores. However, the anaerobic photo- 

 oxidation of particle-bound iron protein has not yet been observed 

 because, unlike the cytochromes, the protein lacks distinctive absorp- 



