SUPPLEMENT 65 



377). This is carried out in the cell, as BUCHNER (1897) has shown, by means 

 of an enzyme, zymase or alcoholase. The existence of this enzyme can be 

 as yet proved only in the same way as those concerned in respiration ; the 

 sugar has been shown to split into alcohol and carbon-dioxide, on the one 

 hand by sap expressed from yeast which has been subjected to great pressure 

 and vigorous trituration, and on the other by intact and rapidly-dried yeast 

 cells, killed by ether or acetone (ALBERT, 1901), just as well as by living yeast. 

 The enzyme, so long as the cell-wall be complete, cannot diffuse out of either 

 the living or the dead cell. As in the case of other enzymes, it loses its charac- 

 teristic properties when treated with certain poisons. In all probability the 

 enzyme is nothing more than a catalytic agent. Hence we meet here with 

 a new type of enzyme, which differs from the hydrolytic and oxidizing ones 

 by its reaction, viz. a profound splitting effect. 



According to BUCHNER and MEISENHEIMER (1905) the splitting of glucose 

 into alcohol takes place through the intermediate body, lactic acid : 



COH . (CHOH) 4 . CH 2 OH = (COOH . CHOH . CH 3 ) 2 

 COOH . CHOH . CH 3 = C0 2 +CH 2 OH . CH 3 



Hence lactic acid when added to the expressed sap should be transformed 

 into alcohol and carbon-dioxide. According to WOHL (1907) methylglycoxal 

 and glycerine-aldehyde occur as intermediate products between sugar and 

 lactic acid and the latter is further changed into methylglycoxal. 



There can be no doubt that the determination of the existence of alcoholases 

 by BUCHNER is one of the greatest advances as yet made in the physiology of 

 fermentation ; it is worthy of note, however, that already E. TRAUBE (1858) 

 had suggested that ' enzymes ' were the cause of fermentation, although he 

 was not successful in isolating them from the living substance. 



Although the existence of alcoholase has been proved, alcoholic fermenta- 

 tion by no means loses the character of a vital process, for zymases, as well 

 as enzymes, are entirely dependent on the organism both in their origin and 

 activity. If we could obtain alcoholase pure we would probably be able to 

 demonstrate that its activity was dependent on external conditions in a quite 

 different way than is fermentation in the living cell. Thus it is very probable 

 that the optimal temperature for zymases is much higher than that for the 

 fermenting cell. We cannot, however, prove that exactly, because the zymase 

 in the expressed sap is destroyed by a proteolytic enzyme operative at the 

 same time, all the more rapidly the higher the temperature is (BUCHNER and 

 HAHN, 1903, p. 149). Further, it is known that zymase is active in sugar 

 solutions of high concentration, while fermentation ceases entirely in a cane- 

 sugar solution of at most 35 per cent. The most remarkable fact finally is the 

 difference between enzymes and living cells in their dependence on oxygen. 

 The enzyme splits the sugar independently of the presence of oxygen, while 

 cells in this respect vary in their behaviour. Thus, in the last lecture, we got 

 to know of higher plants and Fungi, where alcohol was formed only when 

 oxygen was excluded, i.e. in intra-molecular respiration. In this case zymase 

 has, perhaps, not yet been demonstrated with certainty (STOKLASA, 1904 ; 

 MAZE, 1904), still its existence cannot be doubted. We do not know, however, 

 in what relation it stands to the respiratory enzymes, whether it is in part 

 identical with them or whether it is quite distinct from them. In the first 

 case, the difference between intra-molecular and normal respiration must be 

 that the primary products of splitting must be used up further in the presence 

 of oxygen than in its absence ; in the second case, on the other hand, the 

 absence of oxygen must increase the activity of the zymase, while in ordinary 

 cases an oxidase would be operative. 



Still all organisms do not behave in this way. We owe to PASTEUR (1861 

 JOST E 



