MACROMOLECULES 



91 



(c) Polyglucosamines 



Chitin, a constituent of fungi and of the exoskeleton of arthropods, 

 falls into this category. 



Hydrolysis with boiling acids gives glucosamine and acetic acid in equiva- 

 lent amounts. A more careful hydrolysis with chitinase gives as the sole pro- 

 duct N-acetylglucosamine, that is, glucosamine acetylated at its amino group. 



It has been possible to isolate from the products of a mild hydrolysis a 

 disaccharide, chitobiose, identical with cellobiose except that C-2 of each 

 glucose unit bears an amino group. 



(»). 



(b) 



(a) Cellulose 



CHjOH 



(b) Chitin 



R = CH3CO— (acetyl) 



B. Heteropolysaccharides 



{a) Gums and Mucilages 



It is difficult to make any definite distinction between these two classes 

 of macromolecules. Gums, which exude from bark in the form of "gum 

 arable", are salts of heteropolyuronides. Mucilages, like that from linseed, 

 swell in water. In both cases we are dealing with highly complex branched 

 molecules containing several sugars. For example, in gum arable, arabinose, 

 galactose, rhamnose, glucuronic acid, etc., are all present, whilst in the 

 mucilage of the plaintain seed the following substances have been detected : 

 galacturonic acid, rhamnose, galactose, arabinose, xylose, etc. 



(6) Mucopolysaccharides 



These polysaccharides are invariably associated with amounts of protein 

 which, although they are small, are always present and are by no means 

 negligible. 



1. Hyaluronic acid 



This polysaccharide is very widely distributed, both in the free form and as 

 salt-like compounds with proteins. It is the inter-cellular cement in animals. 



Hyaluronic acid is a complex polysaccharide containing equivalent 

 amounts of D-glucosamine, D-glucuronic acid and acetic acid combined 

 with glucosamine in the form of N-acetyl-D-glucosamine. 



