226 



Paulette Chaix 



If these yeasts are harvested during the exponential phase of growth their 

 reduced haematin spectrum is characterized at low temperature by three 

 a-bands situated at 552-5 mjii, 558 m// and 574-5 m// (Fig. 1, curve 1) (Chaix 

 and Heyman-Blanchet, 1957). 



575 600 



A. m/^ 



Fig. 1. Progressive change of the haematin spectrum of yeast cultured anaerobic- 

 ally on a yeast extract medium as a function of growth phase. Optical density of 

 the culture was read at the time of harvesting. Reduction by endogenous substrate. 

 For definition of the CU unit, see text below. (1), 64 CU; (2), 102 CU; 

 (3) 120 CU; (4), 178 CU. 



If the yeast is harvested after the exponential phase of growth the observed 

 spectra change as the growth rate slows down. 



When the culture reaches 102 CU (one CU unit means the optical density, 

 measured with the Coleman photometer, which corresponds to 17-1 //g dry 

 weight of yeast/ml), the three a-bands (spectrum 2) present during the expo- 

 nential phase persist, but the band at 574-5-575 m/f has been accentuated; 

 moreover two rather faint new bands have commenced to appear of which 

 one, situated at 585 m//, has already been observed by Lindenmayer and Smith 

 (1957); the other is situated at 630 m^. This last component does not seem 

 to correspond to catalase since the catalatic activity of anaerobic yeast is 

 very low. 



