CARBOHYDRATES J] 



Derived Adds 



The oxidation of the aldehyde group of the aldoses yields polyhy- 

 droxycarboxylic acids, called by the general name glyconic acids. 

 Gluconic acid is the specific compound of this type resulting from 

 D-glucose and is formed by certain bacteria. A derivative, phospho- 

 gluconic acid, is a key metabolic intermediate in a number of species. 

 Other acids of this type have been synthesized in the laboratory, but 

 nothing is known of the biology of these substances. 



The glycuronic acids include the compounds with the other end of 

 the molecule oxidized. Glucuronic acid, for example, has the structure 

 shown and as expected exhibits mutarotation and reducing properties. 



COOH 



H OH 



glucuronic acid 



With the additional functional group, new types of reactions are pos- 

 sible. This acid has been mentioned as a component of mucoitin 

 and chondroitin sulfuric acids and hemicellulose. It occurs in various 

 gums like gum arable and a variety of polysaccharides. In addition, 

 animals and man synthesize glucinonic acid and esterify it with a 

 number of toxic products which can then be excreted harmlessly in 

 the urine. The body thus disposes of phenol, cresol, indoxyl, and simi- 

 lar otherwise dangerous hydroxy compounds. 



The related galacturonic acid also is found in polysaccharides but is 

 best known from pectin, the gel-forming material of jams and jellies. 

 Pectin is a polymer of the methyl ester of galacturonic acid with the 

 units linked at the 1,4 positions. Alkaline solutions split the ester 

 groups, yielding methanol and the salt of pectinic acid, the macromole- 

 cule still with the basic structure of pectin itself. Pectin is usually ac- 

 companied by polysaccharides made up of L-arabinose and D-galactose 

 and is associated with them in practical usage. 



Dicarboxylic acids called saccharic acids are formed when both ends 

 of aldoses are oxidized. Little is known of the biochemistry of these 

 compounds. 



