The alcoholic enzyme. The enzyme that converts sugar into alcohol and carbon dioxide has been only recently discovered, although it has been diligently sought for since the time of Pasteur. The discovery of Buchner in 1896 that, by applying great pressure to a mass of yeast cells, an enzyme, which he named zymase, could be extracted gave in fact a new impulse to all enzyme study. Zymase appears to dislocate the sugar molecule according to the classic formula:
| C6H12O6 | 2C2H5OH | 2CO2 | ||
| dextrose | alcohol | carbon dioxide | ||
| 180 gr. | 92 gr. | 88 gr. |
The explanation of the prolonged failure of investigators to discover zymase lies in the fact that this enzyme is closely associated with the substance of the living yeast cell and does not diffuse out into the surrounding medium as does another common yeast enzyme already mentioned under the name of invert-ferment or sucrase. In solution, zymase quickly loses its strength, probably partly because of oxidation, partly because of the destructive action of the tryptic enzymes of yeast. Zymase is able to convert a number of different sugars into alcohol and carbon dioxide: maltose and sucrose are readily fermentable, galactose much less readily and lactose not at all. Glycogen can be slowly fermented by zymase, but is not fermented by the living yeast cell because it can not pass through the cell-membrane into the cell and zymase can not pass out. The brilliant researches of Emil Fischer upon the relation of the configuration of the sugar molecule to its fermentability have demonstrated how delicate is the relation obtaining between the structure of the sugar molecule and the enzyme that attacks it. A slight rearrangement in the position of the atoms within the molecule, the actual number of atoms remaining all the while the same, is sufficient to determine whether a sugar can be fermented or not. Only in those cases where the geometrical build of the enzyme conforms to that of the sugar molecule can fermentation occur. To use Fischer's metaphor, the enzyme must fit the substance it attacks as closely as the right key fits the wards of the lock that it opens.
Other enzymes. A few other important enzymes can be but briefly mentioned, since the limits of this review do not permit of a fuller consideration. A group of enzymes of which emulsin is the type may be classed as the glucoside-splitting enzymes. These ferments are able to split up glucosides—which may be described as compounds of glucose (or some other sugar) with an alcohol, ether, aldehyde, or similar body—into glucose and the aldehyde or other associated compound. Emulsin is found in many plant tissues, but it is doubtful if it occurs in any animal body. The physiological role of emulsin is not wholly understood; it is possible that the glucose formed by the enzyme action is useful in the nutrition of the plant, or it may be true that the toxic
