On the influence of thiamine and ammonium ions on alcoholic fermentation

Abstract

1. 1. In a glucose-sodium acetate medium of pH 5.6 the fermentation rate of bakers' yeast remains constant at a low level during several hours, while in the presence of ammonium sulphate it gradually increases. The rise is steeper in the presence of thiamine.

2. 2. After the ammonium ions have been utilized the rate of fermentation decreases to a level, the height of which depends upon the amounts of ammonium sulphate and thiamine added.

3. 3. In the presence of an ammonium salt not containing assimilable sulphur in its anion a decrease of the fermentation rate occurs before the ammonium ions have been utilized. This decrease is not observed when besides the ammonium salt a suitable amount of sodium sulphate is added.

4. 4. Thiamine and ammonium sulphate exert their effect on fermentation in a sodium acetate medium of pH 5.6, and under these conditions also considerable amounts of protein and carboxylase are formed. When the same buffer salt is used at pH 3.5 the effects of both thiamine and ammonium sulphate on the fermentation rate are absent, and no protein and carboxylase are formed either. In the presence of K2SO4, KH2PO4, Na2SO4 or NaH2PO4, however, the effects of both thiamine and ammonium sulphate on the fermentation rate are also observed at this pH, while under these conditions the synthesis of carboxylase, and consequently the synthesis of protein, also occurs again.

5. 5. An explanation of the phenomena observed in glucose-sodium acetate medium of pH 5.6 containing ammonium sulphate is given.

6. 6. In a glucose-sodium acetate medium of pH 5.6 containing ammonium sulphate and thiamine the maximal amount of carboxylase is formed with concentrations of ammonium sulphate of 0.01 to 0.02% and higher, and amounts of 0.02 to 0.05 μg thiamine per 2 mg yeast, after 2 to 4 hours' fermentation. These data correspond closely to those concerning the effects of thiamine and ammonium sulphate on the fermentation rate.

7. 7. After 6 hours' fermentation in the presence of excess ammonium sulphate (0.1%)—thiamine being absent—the rate of fermentation, the amount of protein, and the amount of carboxylase all appeared to have increased by about 50%, while the number of cells had only increased by about 30% as compared to the control experiment (glucose-sodium acetate).

8. 8. After 6 hours' fermentation in the presence of an excess of both ammonium sulphate and thiamine the rate of fermentation and the amout of carboxylase had once more increased by about 60%, and the number of cells by about 20%, whereas the amount of protein had not more increased than in the presence of ammonium sulphate alone.

9. 9. The effect of thiamine upon the fermentation of bakers' yeast depends quantitatively upon the formation of carboxylase, this enzyme being the limiting factor of fermentation, both in the absence and in the presence of ammonium sulphate.

10. 10. Like bakers' yeast, brewers' yeast also forms carboxylase in the presence of ammonium sulphate. The addition of thiamine to the medium, however, has no influence on the amount of carboxylase formed. The amount of non-carboxylase thiamine pyrophosphate present in the brewers' yeast obviously is sufficient for obtaining the maximal content of carboxylase. This explains why the fermentation of brewers' yeast is not influenced by added thiamine.