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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    d-amyl alcohol when these amino-acids were added in the pure state to a solution of sugar and treated with a considerable proportion of yeast [1905 ; 1906, 2, 3 ; 1907, I, 3]. The chemical reactions involved are represented by the following equations :—- (1) (CHS), • CH • CH2 • CH(NH2) • COOH + HaO = (CH3)2 • CH • CH2 • CH2 • OH + C02 Leucine iS0-amyl alcohol +NH3 (2) CH3 • CH(C2H5) • CH(NH2) • COOH + H,0 = CH3 • CH(C2H5) • CH2 • OH + C02 ^o-leucine d-amyl alcohol +NH3 Ihe experiments by which these important changes were demon- strated were of a very simple and convincing character [Ehrlich, 1907, 1]. Two hundred grams of sugar and 3 to 10 grams of the nitro- genous substance to be examined were dissolved in 2 to 2*5 litres of tap-water in a 3 to 4 litre flask ; the liquid was sterilised by being boiled for several hours, and after cooling 40 to 60 grams of fresh yeast were added and the flask was allowed to stand at room temperature until the whole of the sugar had been decomposed by fermentation. In the earlier experiments the amyl alcohols were isolated and identified by conversion into the corresponding valerianic acids, but as a rule the fusel oil as a whole was quantitatively estimated in the filtrate by the Rose-Herzfeld method [Lunge, 1905, p. 571]. Ihe following are typical results. (1) An experiment carried out as above without any addition of leucine gave 97*32 grams of alcohol containing 0*40 per cent, of fusel oil. (2) When 6 grams of synthetic, optically inactive leucine were added, 97*26 grams of alcohol were obtained, containing 2*11 per cent, of fusel oil, which was also optically inactive ; 2-5 grams of leucine were recovered, so that 87 per cent, of the theoretical yield of isosanyl alcohol was obtained from the 3*5 grams of leucine decomposed. (3) In the presence of 2-5 grams of d-isoleucine (prepared from molasses residues), 200 grams of sugar gave 93*99 grams of alcohol, containing 1*44 per cent, of fusel oil, which was lsevo-rotatory. This corresponds with 80 per cent, of the theoretical yield of d-amyl alcohol from the wHeucine added. This change, which Ehrlich has termed the alcoholic fermentation of the amino-acids, although brought about by living yeast, does not appear to occur at all when zymin [Ehrlich, 1906, 4 ; Pringsheim, 1906] or yeast-juice [Buchner and Meisenheimer, 1906] is substituted for the intact organism, nor is it effected even by living yeast in the absence of a fermentable sugar [Ehrlich, 1907, 1]. The reaction appears indeed to be intimately connected with the nitrogenous metabolism of the cell, and the whole of the ammonia pro'duced is at once assimilated, and does not appear in the fermented liquid. Other oc-amino-acids undergo
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