321 



The Alcoholic Ferment of Yeast-juice. Part V.^ — The Function 

 of Phos'phates in Alcoholic Fermentation. 



By Arthur Harden, F.E.S., and William John Young (Biochemical Laboiatory 

 of the Lister Institute of Preventive Medicine). 



(Received February 12,— Read February 24, 1910.) 



Two equations have been proposed by the authors* to represent the course 

 of alcoholic fermentation by yeast-juice: 



(1) 2C6H12O6+ 2PO4HR2 = 2CO2+ 2C2H6O + 2H2O + CeHio04(P04E2)2, 



(2) C6Hio04(P04R2)2+2H20= C6Ha206 + 2P04HE2. 



These were founded on (a) the determination of the amount of carbon dioxide 

 and alcohol produced by the addition of a known amount of phosphate in 

 presence of excess of sugarf ; (h) the production of a hexosephosphate of the 

 composition C6Hio04 (P04R2)2 ; (c) the occurrence of an enzymic hydrolysis, 

 of this substance with production of free phosphate. 



In order to obtain further experimental justification for this view, several 

 additional determinations have been made, and these form the subject of the- 

 present paper. 



I. Ratio of Carbon Dioxide produced to Sugar fermented in Presence 

 of Excess of Phosphate. 



When glucose or fructose is fermented by yeast-juice in presence of excess^ 

 of phosphate, a period of accelerated fermentation occurs, during which two 

 molecules of carbon dioxide are evolved and one molecule of hexosephosphate- 

 formed from two molecules of sugar added. The ratio between sugar added 

 and carbon dioxide evolved is determined by adding a known weight 

 of sugar, together with an excess of sodium phosphate to yeast-juice at 25°. 

 The phenomena then observed are precisely similar to those which occur 

 when a phosphate is added to a fermenting mixture of yeast-juice and excess of 

 sugar, as previously described {loc. cit.)., The rate of fermentation rapidly rises,, 

 and then gradually falls until a rate is attained approximately equal to that of 

 the auto-fermentation of the juice in presence of phosphate. At this point 

 it is found that the extra carbon dioxide evolved, beyond the amount which 

 would have been given off in the absence of added sugar, is equivalent to- 

 only half the sugar according to the equation: 



CeHiaOe = 2C02-f- 2C2H6O, 



* ' Roy. Soc. Proc.,' B, 1908, voL 80, p. 299. 

 t 'Roy. Soc. Proc.,' B, 1906, vol. 77, p. 405. 



