CARBOHYDRATE METABOLISM 



83 



of alcohol to acetic acid. On the other hand, the products formed 

 may serve as food to other microorganisms and thus be completely 

 oxidized. Acetic acid, if not too strong, may be further oxidized to 

 carbon dioxid and water, as sometimes occurs, resulting in a decrease 

 in the strength of vinegar. 



3. Alcoholic fermentation is brought about by yeast; yet there 

 are bacteria which possess the power of producing alcohol, but none 

 of them are of economic value. Such organisms have been obtained 

 from hay (B. fitizianus] and sheep manure (B. ethaceticus). The 

 Bad. pneumonias of Friedliinder is not only a pathogenic organism, 

 but also possesses the power of decomposing sugar solutions with the 

 formation of ethyl alcohol and acetic acid. 



The reaction as brought about by yeast is due to the endo-enzyme, 

 zymase, first isolated by Biichner. The reaction is dependent upon 

 a readily available supply of phosphate, and according to Harden 

 this forms an intermediate product with glucose, thus: 



2C 6 Hi 2 O 6 



== 2CO 2 



I 



2C 2 H 6 O 

 II 



2H 2 O 



2H 2 O = C 6 Hi 2 O 6 + 2PO 4 HR 2 



According to equation (I), two molecules of glucose are concerned 

 in the change, the carbon dioxid and alcohol being equal in weight 

 to one-half of the sugar used, and the hexosephosphate and water 

 representing the other half. In the second equation the phosphate 

 is again liberated, and the hexose presumably fermented. 



I 



CHO 

 CHOH 



CHOH 



I 

 CHOH 



CHOH 



CH 2 OH 



Glucose. 



IV V 



Methylglyoxal. 

 CHO 



CO + 

 CH 3 



CHO H CHO 



I I 



CHOH OH COH 



I II 



CH 2 OH CH 2 



Glyceraldehyde. 



H 



II 

 CHO 



C(OH) 



CH 



CHOH 



CHOH 



I 



CH-OH 

 Enol form. 



Ill 

 CHO 



CO 



CH 2 



CHOH 



CHOH 



I 

 CH 2 ()H 



Keto form. 



VI 



H 2 O 



VII 

 COOH 



CHOH 

 CH 3 



CHO 

 CO 



CH 3 



Methyl-glyoxal. 



H 2 O 



COOH 

 CHOH 

 CH 3 



VIII 

 CO 2 

 CH 2 OH 

 CH 3 



( '< ), 



CH 2 OH 



CH 3 



Lactic acid. Alcohol and carbon 

 dioxid. 



