Zymase

Main article: Ethanol fermentation

Zymase is an enzyme complex that catalyzes the fermentation of sugar into ethanol and carbon dioxide.[1] It occurs naturally in yeasts. Zymase activity varies among yeast strains.[2]

Zymase is also the brand name of the drug pancrelipase.

Cell-free fermentation experiment

Zymase was first isolated from the yeast cell in 1897 by a German chemist named Eduard Buchner who fermented sugar in the laboratory without living cells, leading to 1907 Nobel Prize in Chemistry.

The experiment for which Buchner won the Nobel Prize consisted of producing a cell-free extract of yeast cells and showing that this "press juice" could ferment sugar. This dealt yet another blow to vitalism by showing that the presence of living yeast cells was not needed for fermentation. The cell-free extract was produced by combining dry yeast cells, quartz and kieselguhr and then pulverizing the yeast cells with a mortar and pestle. This mixture would then become moist as the yeast cells' contents would come out of the cells. Once this step was done, the moist mixture would be put through a press and when this resulting "press juice" had glucose, fructose, or maltose added, carbon dioxide was seen to evolve, sometimes for days. Microscopic investigation revealed no living yeast cells in the extract.

Buchner hypothesized that yeast cells secrete proteins into their environment in order to ferment sugars. It was later shown that fermentation occurs inside the yeast cells.

British chemist Sir Arthur Harden divided zymase into two varieties (dialyzable and nondialyzable) in 1905.

Some science historians[3] suggest that Eduard Buchner, in his 1897 work, merely repeated experiments already made by Antoine Béchamp in 1857. This is not the case : what Buchner obtained with yeast zymase, and without yeast cells, was alcoholic fermentation, while Béchamp had explicitly stated that, in absence of yeast cells, and by use of what he, also, called "zymase", he obtained only sugar inversion and no alcoholic fermentation.[4] According to K.L. Manchester,[5] what Béchamp called "zymase" was invertase.

References

  1. ↑ The enzyme complex in yeasts that catalyzes the breakdown of sugar into alcohol and carbon dioxide." http://www.thefreedictionary.com/zymase
  2. ↑ Angelov, A. I.; Karadjov, G. I.; Roshkova, Z. G. (1996). "Strains selection of baker's yeast with improved technological properties". Food Research International 29 (3–4): 235. doi:10.1016/0963-9969(96)00030-0.
  3. ↑ " Our textbooks, however, erroneously tell us that Buchner was the first to extract an enzyme from yeast, and call it zymase, a 'breakthrough' that was achieved in 1897, some 35 years after Bechamp's experiments ! " (Milton Wainwright, " Early history of microbiology ", Advances in applied microbiology, vol. 52, 2003, pp. 333-355, partly available on Google Books, esp. pp. 341-342.)
  4. ↑ Antoine Béchamp, Les microzymas, Paris, 1883 (repr. Paris, 1990), pp. 286-288
  5. ↑ Keith L. Manchester : " Antoine Béchamp: père de la biologie. Oui ou non? ", Endeavour, Vol. 25, n° 2, 1 juny 2001, pp. 68-73; Keith L. Manchester : " Louis Pasteur, fermentation, and a rival ", South African Journal of Science, vol. 103 (2007), online.