428 LIGHT AND LIFE 



chloroplasts can be observed optically. By jDroviding a suitable op- 

 tical path length it is possible to obtain loAv-temperature spectra 

 of the cytochromes jjresent in freshly prepared whole chloroplasts. 

 Such a spectrum, showing the difference in absorption between illumi- 

 nated and hydrosulfite-reduced chloroplasts, is shown in Fig. 4. In- 

 spection of this figure shows that the cytochrome spectrum of whole 

 chloroplasts only superficially resembles that obtained from 80 per 

 cent acetone-extracted chloroplasts. With the whole chloroplast, the 

 peaks of absorption are shifted to slightly longer wavelengths as 

 compared to the acetone-extracted chloroplasts, and there are several 

 indications that there is present, in whole chloroplasts, a third com- 

 ponent which absorbs at a wavelength intermediate between / and 

 fee- It is concluded here that treatment of green plant chloroplasts 

 with cold 80 per cent acetone does more than remove the chlorophylls 

 and carotenoids. 



The study of cytochromes in chloroplasts has been extended by 

 many workers to algae and bacteria. These studies have been critically 

 reviewed by Smith and Chance (15) . In general, the results of such 



A0D = 0.02 



I 1 1 



500 550 600 



Fig. 4. Low-tcmperatiire difTcrcncc spcctriiin of whole spinach chloroplasts; 

 imtunlc'd — ludrosiilfitcrcdiucc!. 



