CARBOHYDRATES 193 



The Breakdown of Glucose 



Though there are several ways in which glucose oxidation can 

 theoretically take place, it is most probable that the molecule first 

 splits into two molecules, each containing three carbon atoms. 

 These eventually become converted into lactic acid. Lactic acid 

 can be produced by the action of alkalies on glucose ; it is formed in 

 the body when the oxygen supply is inadequate ; it is formed on per- 

 fusion of a liver loaded with glycogen; when given to the normal 

 animal it yields glycogen, and when given to the diabetic animal, 

 glucose. 



The intermediate steps between glucose and lactic acid may 

 probably be represented in this way : — 



(Glucose) 



I 

 CH2OH CHOH CHOH 



CHOH CHOH CHO 



I 

 CHaOHCHOHCHC 



(Glyceric aldehyde) (Glyceric aldehyde) 



I (Glucose) : j 



CH2OHCHOHCHO CH2OHCHOHCHO 



CH3COCHO 



(Methyl glyoxal) 



I 

 CH3 CHOH COOH 



(Lactic acid) 



Each of the above changes can be produced in vitro. Glycerine 

 (though not glyceric aldehyde) when perfused through the liver 

 yields lactic acid. 



The further oxidation of lactic acid occurs probably through the 

 intermediate formation of pyruvic acid, acetaldehyde and acetic acid. 



CH3 CHOH COOH 



Lactic acid. 



I 

 CH3 CO COOH 



Pyruvic acid. 



I 



CH.CHO 



Acetaldehyde. 



CH3COOH 



Acetic Acid. 



CO2 H^O 



It is now known that alcohol is not a usual intermediate compound, 

 13 



