Alcoholic fermentation / by Arthur Harden.

  • Arthur Harden
Date:
1932
Catalogue details

Licence: In copyright

Credit: Alcoholic fermentation / by Arthur Harden. Source: Wellcome Collection.

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    with the juice prepared from top yeast in England, in which the enzyme does not outlast the co-enzyme [Harden and Young, 1907]. The difference may be due to some variation in the relative propor- tions of enzyme and co-enzyme or of the enzymes to which the dis- appearance of each of these is presumptively due, or to a combination of these two causes. It was, however, found, even in the juice from bottom yeast, that incubation for three days at 22° without the addi- tion of sugar caused the disappearance of the enzyme as well as of the co-enzyme and left a residue alike incapable of being regenerated by the addition of co-enzyme or of restoring the power of producing fer- mentation to an inactive mixture containing enzyme and sugar. Nord and Franke [1928] obtained preparations from American bottom yeasts which retained their fermenting powers for two months at 5°-i5°, and increased in activity during the first few days. They attribute the loss of fermenting power to increase in peptisation, and find that exposure of the extract to ethylene “ protects ” the enzyme to some extent. If the fermenting power of the juice is to be preserved by repeated regeneration for a long period, it is absolutely necessary to add the co-enzyme solution each time as soon as fermentation has ceased, since the enzyme in the absence of co-enzyme rapidly disappears, even in the presence of sugar. The processes by which the enzyme and co-enzyme are inactivated are still obscure. On the assumption that the alcoholic enzyme of yeast-juice belongs to the class of proteins, the antiprotease of Buchner and Haehn [1910, 1] (see p. 43) may be supposed to lessen the rate at which this enzyme is destroyed by the proteases of the juice. This antiprotease is more stable than the co-enzyme towards hydrolytic agents, and can be obtained free from co-enzyme by boiling the solu- tion for some hours alone or by heating with dilute sulphuric acid. Such a solution possesses no regenerative power, but still retains its power of protecting proteins against digestion and of preserving the fermenting power of yeast-juice. Kluyver and Struyk [1927 ; 1928, 2] in fact regarded the anti- protease as the essential constituent of the co-zymase (see p. 91), but this has not been confirmed by other workers [see Myrback, 1928 ; Stheeman, 1929, 1930]. It must, however, be remembered that the addition of a phosphate alone may greatly prolong the period of fermentation of yeast-juice (p. 72), and sugar is well known to exert a similar action. It appears, therefore, that the existence of the enzyme is prolonged not only by
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