234 



Discussion 



Chaix: The bands at 575 m/< and 630 mfi do not disappear after incubating the yeast 

 cells for 90 sec at room temperature with dithionite (3 x 10^^ m). Incubation in the 

 same conditions, but with solid dithionite, causes the disappearance of these bands. 

 In the latter case the disappearance may be due to a denaturing effect of dithionite. 



500 



550 



600 



A, rr\// 



Fig. 1. 'Frozen steady-states' of cytochromes c, c^ and b of baker's yeast 



cells. (A) glucose-treated ; (B) ethanol treated ; (C) oxidized-reduced (Expt. 



938-2). Reprinted with permission of the Faraday Society (B. Chance and 



E. L. Spencer, Jr., Disc. Faraday Soc. 27, 200, 1959). 



TissiEREs: Keilin and I have described an absorption band at 583 m/t in several moulds 

 including some strains of yeast; this band appears on aeration, disappears on addition 

 of dithionite and is replaced by a diffuse band at 575 m/t on treatment with CO. The 

 band was therefore attributed to an oxyhaemoglobin. In the slow-growing 'petite 

 colonie' strains which have a very low respiration rate, the oxyhaemoglobin absorption 



