54 A SYMPOSIUM ON RESPIRATORY ENZYMES 



alternating torula or wild yeast type. Baker's yeast is intermediate, 

 having a fair respiration and partially persistent aerobic fermenta- 

 tion. The metabolic type is not rigidly fixed. With aeration there is 

 adaptation to the respiratory type, and with the exclusion of air the 

 reverse is easily achieved (Table 2). It may be noted that the re- 

 appearance of respiration is accompanied by aerobic repression of 

 fermentation. The history of the manufacture of baker's yeast is an 

 impressive illustration of the economic superiority of aerobic me- 

 taboHsm (10). The earlier "Vienna" procedure of growing yeast 



Table 2.— Yeast metabolism 



Type Qo, Q^'f Q^ 



F 



(Q^' f-QQ'f)X3 Inhibition 

 Q02 per cent 



Wild yeast -180 18 260 4 93 



Baker's yeast -87 95 274 6.2 65 



Brewer's yeast -8 213 233 7.5 8 



Same after 15 hours aeration -73 113 193 3.3 42 



without agitation has now been almost entirely replaced by the 

 aeration procedure, for it has been found that through aeration the 

 yield can be greatly increased with the same amount of culture 

 fluid. In metabolic terms, the same amount of metabolized substrate 

 yields a larger amount of yeast material with economical respiration 

 than with uneconomical fermentation. 



As a measure of the Pasteur effect two differently derived units 

 are recorded in the last two columns of Table 2. In the first of the 

 two the Meyerhof Oxidation Quotient is calculated. This relates the 

 disappearance of fermentation to the magnitude of respiration. 

 When three times the difference between fermentation in nitrogen 

 and fermentation in oxygen is divided by the respiration in oxygen, 

 the quotient represents the relation between the glucose equivalent 

 of fermentation and that of respiration. Disregarding underlying 

 theoretical implications, it states how much fermentation glucose 

 is replaced by oxidized glucose when respiration is allowed to occur. 

 Stressing the economical significance of the quotient, we have pro- 

 posed to call it a replacement quotient (3). In the next column the 

 percentage of inhibition is calculated. From the recorded figures one 

 would suspect a relationship of some kind between the magnitude 

 of respiration and the Pasteur effect. This observation originally led 

 Meyerhof to a universal application of his resynthesis theory as an 

 explanation of the Pasteur effect. 



