ANTIGENS AS BIOCATALYSTS 



17 



(+110°) into /3-glucose (+19°), and vice versa, until an equilibrium 

 (at +52.5°) is established, i.e. a-glucose ^ ^S-glucose. In a-glucose the 

 hydroxyl groups at Ci and C2 are in cis-, and in /?-glucose in trans- 

 positions. The mechanism of the interconversion of d-glucose, a-d- 

 glucose, and ^S-d-glucose has been extensively studied. 



The mutarotation of glucose involves the reversible change of one 

 stereoisomeric form of glucose into another which differs only in the 

 spatial arrangement of the groups attached to the carbon marked 

 with *. This reaction requires the breaking and the reformation of one 

 of its bonds. It has been shown that it is not the carbon to hydrogen 

 link which has been severed, for if the mutarotation takes place in D2O 

 this hydrogen is not exchanged by deuterium. It has therefore been 

 assumed that the ether oxygen to carbon link is involved in this con- 

 version. According to the general acid-hase catalysis the reaction 

 proceeds in the following manner. 



H O— H 



HO-O 10— H 



HO— G C— CH2OH 



\/^H 



/^ 

 H OH 



+ 



+ A- 



i 



H O 



\ 



H. 



HO— C 

 HO— C 



10— H 



+ HA 



\/ ^H 

 H OH 



C— CH2OH 



In the acid catalysis there is mobile and reversible addition of a H+ 

 to the ether oxygen which is followed by a comparatively slow reaction 

 with a base (A") producing the symmetrical carbonyl form. While in 



