212 P. P. Slonimski and H. de Robichon-Szulmajster 



has committed himself to one of those, in an effort to explain 

 the poor adaptability to oxygen of exponential anaerobic 

 yeast by a deficiency in the free amino-acid pool (Slonimski, 

 1956). Subsequent experiments have shown that this explana- 

 tion was wrong. Anaerobic incubation in glucose-containing 

 buffer may be sufficient to restore adaptability. We started 

 naively to investigate the eff'ect of some carbohydrates and 



C HO C HO 



I I 



HO— C— H H— C— OH 



I I 



HO— C— H H— C— OH 



I I 



CHg- OH CH2— OH 



L Erythrose d 



CHO CHO 



I I 



H— C— OH HO— C— H 



I I 



HO— C— H H— C— OH 



I I 



CH2— OH CH2— OH 



L Threose d 



Fig. 1. C4 Sugars. 



their derivatives and found a batch of deoxyribose that had a 

 very strong stimulatory effect on adaptation. 



We have eliminated the 2-deoxy-D-ribose which is without 

 effect, and tracing impurity after impurity we have arrived 

 at C4 sugars : tetroses. Four members of this class are known 

 (Fig. 1). Three of them are found to be inactive; the fourth, 

 D-threose, has not yet been investigated. However, it is 

 possible to synthesize from pure tetroses by a relatively mild 

 chemical treatment certain compounds that have novel 

 biological activity. We shall call them cofactors, those 

 deriving from erythrose will be designated by E and those 



