THE CARBOHYDRATES AND THEIR METABOLISM 225 



Since there are two closed ring forms for each aldohexose, the a and 

 (3 forms, there should be 32 closed chain aldehexoses, 4 with which the 16 

 already discussed make a total of 48 isomeric aldohexoses theoretically 

 possible. Most of the carbohydrates exist in more than one form and 

 possess the power of mutarotation. 



TABLE III 

 SPECIFIC ROTATIONS OF SUGABS 



a Methyl glucoside 4-157. /3 Methyl -glucoside 33. 



Chemical Reactions of the Carbohydrates 



In most cases glucose will be used as a typical carbohydrate in dis- 

 cussing the reactions which the carbohydrates undergo. (Only those that 

 have a direct interest to the biochemist will be presented.) 



Synthesis and Degradation of Carbohydrates. Most of the methods 

 of synthesizing the carbohydrates we owe to the masterly researches of 

 Emil Fischer, who devised most of the methods and synthesized a vast 

 number of them. 



1. Polymerization (aldol condensation) of simple sugars by action 



of dilute alkali, e.g., 



2 C 3 H C 3 

 Glycerose 



C C H 12 

 Fructose 



This reaction is somewhat similar to one by which it is believed carbo- 

 hydrates may be formed in plants from formaldehyde. Baeyer, in 1870, 

 first advanced the theory that the plant tissues formed formaldehyde from 

 CO 2 and H 2 O. Loew, in 1886, discovered that formaldehyde (H( 

 and lime water at room temperature produced a sweet substance which was 

 unfermentable. Fischer later showed that what is formed here is a acrose, 



In the closed chain formula there is an additional asymmetric carbon atom, so 

 that the number of isomers is 2 5 or 32. 



