ZYMASE 487 



more particularly in the fermentation of the sugars obtained 

 from wheat and potato starch. Alcoholic fermentation is due 

 to the activity of the enzyme zymase which was first separated 

 from the yeast cell by Buchner, whose work * marks the 

 beginning of an epoch of vigorous investigations into this and 

 kindred subjects. 



The occurrence of zymase is not confined to 5. cerevisece, 

 which as a result of selection and high cultivation is able to 

 produce a maximum alcoholic fermentation. This activity, 

 which in cultivated yeast is not dependent upon atmospheric 

 oxygen, preponderates over the ordinary aerobic respiration 

 of the plant : in wild yeasts, however, the conditions are re- 

 versed ; these plants respire oxygen freely and only manifest 

 slight fermentative activity. Although oxygen is not neces- 

 sary for alcoholic fermentation, yeasts are not disturbed in 

 this activity by free aeration, the only effect of which is to 

 stimulate their growth and reproduction, while they continue 

 to form alcohol. 



Zymases have also been identified in other Fungi such as 

 Mucor stolonifera-f and Aspergillus niger.X Germinating seeds 

 in the absence of air produce appreciable quantities of alcohol 

 and have been shown to yield a juice containing zymase ; on 

 admitting air the alcohol, if formed, does not accumulate, and 

 there is an increased output of carbon dioxide as compared 

 with the anaerobic condition. 



The Activity of Different Species of Yeast. 



Saccharomyces cerevisecs is the species of yeast employed 

 commercially in the production of alcohol from a sugar 

 solution ; this yeast secretes a number of enzymes in addition 

 to zymase such as invertase, maltase, amygdalase, trypsin, 



protein molecule, by loss of COo and replacement of the NH^ group by OH 

 (see p. 451). The mixture is optically active owing to the asymmetric 

 carbon atom of the secondary butyl carbinol. 



The succinic acid likewise is formed not from carbohydrate, but from 

 the amino acid, glutamic acid, supplied by the protein present. 



* Buchner : " Ber. deut. chem. Gesells.," 1897, 30, 117, mo ; 1898, 

 31, 568. Buchner and Rapp : id., 1897, 30, 2668 ; 1898, 31, 209, 1084, 

 1090 ; 1899, 32, 127. 



t Kostytschew : " Ber. deut. bot. Gesells.," 1904, 22, 207. 



J Maximow : id., 1904, 22, 225. 



