Alcoholic fermentation / by Arthur Harden.

  • Arthur Harden
Date:
1932
Catalogue details

Licence: In copyright

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

    114/258 page 104
    Further proof is afforded by the fact that the corresponding acid is not formed. 2. The product of reaction, when its constitution admits of it, is often optically active, showing that the reduction is carried out by an asymmetric agent and is therefore, probably, a true enzyme reaction. Nearly all these reductions have been effected in the foregoing way, but the addition of sugar is not always essential. Thus a yield of over 50 per cent, of butylene glycol was obtained from aldol by the action of a total of 1550 g. of yeast during two months on 100 g. aldol without any addition of sugar. It must be remembered, however, that this quantity of yeast might contain a large proportion of glycogen (10-30 per cent.) which would gradually undergo autofermentation. Mechanism of the Reductions Effected by Yeast. It may be regarded as established that the source of the hydrogen used up in the various reductions described above is either water (Bach), in which case some acceptor for the oxygen must also be present, or an oxidisable substance, which is directly capable of losing hydrogen (Wieland) and thus acts as a hydrogen donator, and great interest attaches to the nature of this compound. Some light is thrown on this problem by the experiments of Harden and Norris [1914, 1915, see also Harden and Macfarlane, 1931] who showed that dried yeast and zymin lost the power of reducing methylene blue when they were thoroughly washed, but that this power was restored by the addition of the washings, of ordinary bouillon (peptone-beef-broth) and of lactic acid. It is to be presumed that the active substances which restored the power of reduction were capable of acting as oxygen acceptors (or hydrogen donators) and thus enabled the oxido-reduction to proceed. The reaction is evidently highly specific, as many easily oxidisable substances were inactive, including formaldehyde, which acts as the oxygen acceptor in Schardinger’s reaction in milk. These experiments, however, do not indicate what is the actual substance which undergoes oxidation in the various phytochemical reductions enumerated above, and in order to understand this it is necessary to consider the results obtained by Neuberg and his col- leagues, which are discussed later on (p. 130). It has been shown by them that in all probability the production of alcohol and carbon dioxide from yeast proceeds by way of pyruvic acid, which is then decomposed by the carboxylase of the yeast (p. 93)
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