The Equation of Alcoholic Fermentation.

An equation can readily be constructed for the reaction in which hexosephosphate is formed, the data available being the formula of the product and the relation between the phosphate added and the carbon dioxide and alcohol produced:—

(1) 2 C₆H₂O₆ + 2 PO₄HR₃ =
2 CO₂ + 2 C₂H₆O + 2 H₂O + C₆H₁₀O₄(PO₄R₂)₂.

According to this, two molecules of sugar are concerned in the change, the carbon dioxide and alcohol being equal in weight to one [p052] half of the sugar used, and the hexosephosphate and water representing the other half.

Additional confirmation of this equation is afforded by the determination of the ratio between sugar used and carbon dioxide evolved when a known weight of sugar together with an excess of phosphate is added 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 described above. The rate of fermentation rapidly rises and then gradually falls until a rate is attained approximately equal to that of the autofermentation of the juice in presence of phosphate. At this point it is found that the extra amount of carbon dioxide evolved, beyond that which would have been given off in the absence of added sugar, bears the ratio expressed in equation (1) to the sugar added [Harden and Young, [1910, 2]]. The results of four estimations made in this way were (a) 0·2 grams of glucose gave 26·5 and 27·9 c.c. of carbon dioxide at N.T.P.; (b) 0·2 grams of fructose gave 27·9 and 28·9 c.c. The carbon dioxide calculated from the sugar added in each of the four cases is 26·96 c.c.

It has also been shown by Euler and Johansson [[1913]] that in the fermentation of a mixture of equivalent amounts of phosphate and glucose, the whole of the glucose had disappeared when the whole of the phosphate had become esterified.