NONHEME IRON PROTEINS 321 



Chromatium ivo)i protein amino acid analysis 



- Tryptophan was determined by differential titration with N-brom-succinimide 

 according to the method of Patschornik et al. (17). A valueof 3 yumolestryp- 



/tophan per 9 mg protein was obtained. 

 ~ Amino terminal amino acid was determined by the DNP method of Sanger 

 x/(18). 



- Carboxyl terminal amino acid was determined by the modified hydrazinolysis 

 method of Bradbury (19). 



Interaction Between Iron Protein and Chromatophores. 



When a mixture of washed, dialyzed Chromatium chromatophores 

 approximately 7 /iMinbacteriochlorophyll, together with approximately 

 0.4 mg/ml reduced iron protein in phosphate buffer, was illuminated 

 in the spectrophotometer by far red light ( \ 720 rn.ii, 10 mwatt/cm2), 

 a change in the absorption spectrum occurred which indicated that the 

 iron protein had been converted to the oxidized form, as shown in 

 Fig, 3. The analogous difference spectrum for illuminated-minus-dark 

 anaerobic reaction mixture is shown in Fig, 4. The initial reaction 

 rate in the first experiment was about 15 per cent of the total absorb- 

 ancy change per minute, but the rate rapidly decreased and about 45 

 minutes were required for the reaction to reach the state where nearly 

 quantitative photooxidation of the iron protein had occurred. When the 

 samples were placed in the dark the starting spectrum slowly returned. 

 The light and dark cycle was repeated several times with apparent 

 complete reversibility. Evidently the iron protein underwent anaerobic 



