228 Paulette Chaix 



following with the aid of low temperature spectra the progressive transforma- 

 tion of the anaerobic spectrum into the classical aerobic spectrum in yeast 

 harvested either in the exponential or in the stationary phase. The results 

 of these experiments are shown in the series of curves of Figs. 2 and 3. 



It may be seen that the induction by oxygen is slower when the yeast is 

 harvested in exponential phase than when it is harvested in stationary phase. 

 In each of these two cases the order of disappearance or appearance of bands 

 is quite definitive. In the first case the ca and (a + ^3) a-bands appear 

 progressively without disappearance of the bands at 552-5 and 558 m/t. In 

 the second case the induction begins with the appearance of the bands at 

 552-5 and 558 m/<, followed by appearance of the ca and {a + ^3) a-bands 

 while all the other bands weaken and disappear. It is striking to find that in 

 the classical aerobic spectrum the c^a and ba. bands occupy the same positions 

 as the components of the anaerobic spectrum situated at 552-5 and 558 m/i. 

 The question arises as to whether the q and b components are identical with 

 or superposed on the anaerobic components. 



FRACTIONATION OF YEAST CELLS IN THE EXPONENTIAL 

 PHASE OF AEROBIC AND ANAEROBIC GROWTH; LOCAL- 

 IZATION OF HAEMATIN ENZYMES IN THE DIFFERENT 



FRACTIONS 



(a) Preparation of Yeast Protoplasts 



The yeast was harvested when the culture had reached 50 CU ; in other 

 words, before the last division of the exponential phase of growth. It was then 

 washed by centrifugation in a solution of 0-25 m lactose, and resuspended, at 

 a concentration of 34 mg dry weight/ml in the same lactose solution to which 

 digestive juice of Helix pomatia had been added at a level of 0-025 ml/ml of 

 suspension (Giaja, 1919, 1922; Eddy and Williamson, 1957). On incubation 

 at 25°C for 1-5 hr with gentle shaking, the snail digestive juice brings about 

 enzymic degradation of the yeast cell membranes. A mixture is thus 

 obtained of protoplasts, intact cells with their membranes partly degraded, 

 and cellular debris. The latter is removed by centrifugation for 15min at 

 1000 X g; the pellet is resuspended in 0-5 m lactose and recentrifuged. 



(b) Disruption and Fractionation 



The final pellet, consisting of protoplasts and intact cells, is suspended in a 

 7-5% solution of polyvinylpyrrolidone and disrupted in a Virtis Homo- 

 genizer. The homogenization is carried out in two steps ; a first treatment for 

 10 min at medium speed (rheostat at division 75), and then, after standing 

 for 10 min to allow penetration of the medium into the cells, a further treat- 

 ment for 10 min at medium speed. 



The homogenate so obtained is fractionated by centrifugation as follows : 



