ALCOHOLIC FERMENTATION 267 



Tlie ratio of mono- and di-hexose pliospJiate.s found in 

 fermentation mixtures is very variable, and depends on 

 the strain of yeast and on the concentration of the yeast 

 or yeast preparation used. Living yeast is found not to 

 ferment added hexose diphosphate, and also leads to the 

 formation of only a small amount of it during fermenta- 

 tion. Consequently Harden and Young's equations are 

 almost certainly not a true representation of the mechan- 

 ism. It has been suggested by Kluyver and Struyk and 

 by Meyerhof that the real intermediate is the monophos- 

 phate, and that the diphosphate is a by-product formed 

 either by further phosphorylation of the monophosphate 

 or by condensation of two molecules of a triose mono- 

 phosphate, which also plays a part in the fermentation 

 scheme. Hexose diphosphate, however, plays an essential 

 part in the fermentation reactions. 



Co-enzyme. — It was mentioned on p. 263 that the 

 accelerating effect on fermentation of the addition of 

 boiled yeast juice was traced to two factors, inorganic 

 phosphates and the co-enzyme. It was found that if 

 yeast juice was dialysed or submitted to filtration through 

 porcelain candles it could be divided into two fractions, 

 neither of which alone could induce fermentation of 

 sugar, but which when remixed were once more active. 

 The residue after dialysis or filtration was heat labile and 

 destroyed by boiling ; as was to be expected it contained 

 the undialysable enzjnnes of the yeast juice. The dialysate 

 or filtrate, on the other hand, was heat stable, and was 

 termed co -enzyme or co -zymase. Besides the above- 

 mentioned method for its separation, co-enzyme can also 

 be obtained by washing acetone dried yeast, zymin, with 

 water. 



Subsequent investigations have shown that the 

 co-enzjmae, now known as co -enzyme I, consists of two 

 parts, a magnesium salt and diphosphopyridine nucleo- 

 tide : — 



