54 



Microscopic Histochemistry 



In the case of polysaccharides, treatment with periodic 

 acid will not cause depolymerization of the molecule because 

 the carbohydrate units remain connected by C1-C4 linkages, 

 as indicated in the following scheme: 



HC: 



HCOH 



HOCH O 



HC 



HC- 



HC: 



HCOH 



HOCH O 



0\ 



HC 



HC- 



HC: 



HC=0 



> HC=0 O 



0\ \ 



HC 



HC- 



HC: 



HC=0 



HC=0 O 



0\ 



HC 



HC- 



0\ 



'^% 



CH2OH 



CHsOHi 



CH2OH 



W ' 



CH2OH 



The hydroxyl and/or amino groups must be free to be 

 attacked by periodate; if they are tied down by substitution 

 or by any kind of linkage, the compound will not be touched. 

 The scheme is very general and applies to all sorts of com- 

 pounds possessing vicinal -OH or -OH and -NH2 groups, 

 whether or not they are of carbohydrate nature. Some of the 

 noncarbohydrate substances oxidized to aldehydes are the 

 amino acids serine, threonine, and hydroxylysine. The first 

 two would not be attacked while incorporated within pep- 

 tide chains unless they occupied a terminal position and were 

 thus engaged through their carboxyl groups only. Some car- 

 bohydrates are not attacked because they lack the vicinal 

 -OH groups ( desoxyribof uranose ) ; in other cases the indi- 

 vidual sugar molecules do have such groups, but they are 

 tied down in polymeric linkages; (ribose nucleic acids; C3- 

 Hnked polymers such as agar^ or heparin).^ But even sugars 

 which seem to possess all the necessary prerequisites for 



8. Jones, W. G. M., and Peat, S.: J. Chem. Soc., p. 225, 1942. 



9. Meyer, K.: Ann. New York Acad. Sc, 52:943, 1950; Meyer, K., and 

 Odier, M.: Experientia, 2:311, 1946. 



