ROliERT HILL AND WALTER D. BONNER, JR. 427 



tions shows a marked asymmetry on the short-wavelength side. This 

 same figure (Fig. 2) also shows an oxidized — reduced spectrum of 80 

 per cent acetone-extracted chloroplasts in which the two cytochromes, 

 / and 6j;, are clearly illustrated. The ratio, b^/f, over several experi- 

 ments, was 1.3. 



The spectrum of cytochrome j, present in 80 per cent acetone- 

 extracted chloroplasts, is given in Fig. 3. This same figure has for 

 comparison a spectrum of cytochrome c. Both of these spectra are 

 difference spectra, oxidized — reduced. 



It is very clear from the investigations presented above that the 

 chloroplasts of higher plants contain at least two cytochrome com- 

 ponents, and that these comj^onents are present in relatively high 

 concentration. Since acetone extraction destroys the reactions that 

 are characteristic of isolated chloroplasts and changes the oxidation 

 state of the chloroplast cytochromes, it becomes necessary to refine 

 the techniques to the point where cytochrome components in whole 



ZiO.D = 0.04 



I 



A O.D.=O.OI 



i 



400 



450 



I — I — 

 500 



550 



;^(m>i) 



Fig. 3. Low- temperature difference spectrum of 80 per cent acetone-extracted 

 spinach chloroplasts, oxidized (chlorox) — untreated, showing the characteristic 

 spectrum of cytochrome /. For comparison, an oxidized — reduced difference spec- 

 trum of cytochrome c (dotted line) is included. 



