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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    acids with evolution of carbon dioxide [see Neubauer and Fromherz, I911) p- 35° 5 Neuberg and Kerb, 1912, 4 ; Kostytschev, 1912, 2]. This scheme has been differently elaborated by different workers. According to the simple form suggested by Kostytschev it involves (1) the production of pyruvic acid from the hexoses, a process accom- panied by loss of hydrogen ; (2) the decomposition of pyruvic acid into acetaldehyde and carbon dioxide ; and (3) the reduction of the acetal- dehyde to ethyl alcohol:— (1) C6H12Or> = 2CH3 • CO • COOH + 4H. (2) 2CH3 • CO • COOH = 2CH3 • CHO + 2COa. (3) 2CH3 • CHO + 4H = 2CH3 • CH2 • OH. Neuberg and Kerb [1913, 2] on the other hand propose a more complicated scheme, according to which methylglyoxal is the starting- point for the later stages of the reaction. Moreover, the various oxida- tions and reductions involved are all assumed to be carried out by Cannizzaro transformations, or as the authors term them dismutations, of the aldehydes which are formed as intermediate products. (a) The sugar is split up into two molecules of methylglyoxal, the process probably taking place in two stages : C6H1206 - 2H30 = C6H804 = 2CH2 : C(OH) • CHO Methylglyoxal or aldol. 2CH3 • CO • CHO Methylglyoxal. (b) A portion of the methylglyoxal is converted by a Cannizzaro transformation into glycerol and pyruvic acid : CH2 : C(OH) • CHO + HaO H2 CH2(OH) • CH(OH) • CH2(OH) glycerol + = + CH2 : C(OH) • CHO O CH2 : C(OH) • COOH Pyruvic acid. (c) The pyruvic acid is then decomposed by carboxylase yielding aldehyde and carbon dioxide : CH3 • CO • COOH = CH3 • CHO + C02. (d) The aldehyde and a molecule of methylglyoxal then undergo a Cannizzaro reaction and yield alcohol and pyruvic acid : CH3 • CO • CHO O CH3 • CO • COOH T | — + CH3 • CHO H2 CH3 • CH2(OH) and the latter then undergoes reaction (c). A small amount of glycerol is thus necessarily formed, as is actu- ally found to be the case. I. As regards the production of pyruvic acid from the hexoses by yeast, Fernbach and Schoen [1913 ; 1914 ; 1920 ; 1922 ; Fernbach, 1916]
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