ZYMASE 497 



the optimum concentration of phosphate for the fermentation 

 of fructose is from 1-5 to 10 times as great as the optimum 

 for glucose, and the maximum rate of fermentation of fructose 

 is 2 to 6 times as great as that of glucose. 



Harden and Young also find that the addition of a suit- 

 able amount of arsenate to a fermenting mixture of yeast- 

 extract and sugar (glucose, fructose, or mannose) causes a 

 marked acceleration in the rate of production of alcohol and 

 carbon dioxide, which is continued long after a chemical 

 equivalent of carbon dioxide has been evolved. In this, the 

 action of arsenate differs from that of phosphate and, further, 

 the arsenate occurs in the free state throughout the period of 

 fermentation. This increased rate of fermentation is due to 

 the accelerating influence of the arsenate on the hexose-phos- 

 phatase ; the arsenate, however, cannot replace phosphate in 

 the fundamental reactions of alcoholic fermentation.* 



Whilst it is difficult to explain the precise significance of 

 phosphorus in alcoholic fermentation, it is interesting to note 

 that Embden and his fellow-workers f have found that 

 phosphoric acid is formed simultaneously with lactic acid 

 during muscle contraction, and have traced the formation 

 of these two acids to the same precursor, lactacidogen, which 

 substance they consider to be identical with the hexosediphos- 

 phate of zymase fermentation. The conclusion is not un- 

 warranted that the formation of phosphoric acid esters is an 

 intermediate stage in the metabolism of carbohydrates both 

 in the plant and in the animal. 



That phosphate is a necessity for alcoholic fermentation by 

 zymase is generally agreed, it would not, however, appear to 

 be a requisite in all alcoholic fermentations by the living 

 yeast cell. Thus Euler J finds that top fermentation yeasts 

 do not produce hexose-phosphate, nor do the living yeast cells 

 respond to the addition of phosphate which may be due to 

 the requisite balance naturally obtaining in the plant. 



* Harden and Young : " Proc. Roy. See," B., 191 1, 83, 451. 



t Embden, Griessbach, and Schmitz : " Zeit. physiol. Chem.," 1915, 

 93, I. Embden and Lacqueur : id., 1914, 93, 94 ; 1917, 98, 181 ; 1921, 

 113, I. Embden and Zimmermann : id., 1925, 141, 225. 



X Euler : " Biochem. Zeit.," 1918, 86, 337. 



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