The Chemistry and Biology of Mucopolysaccharides and Glycoproteins

The so-called mucins and mucoids constitute a field common to both protein and carbohydrate chemistry, which has attracted little attention com-pared to that given to the proteins proper. There is at present considerable confusion in regard to terminology and classification i the field. In this paper an attempt will be made to summarize our knowledge of these hexosamine-containing com-pounds of animal origin, to give an account of some of their biological properties, and to classify them according to their known chemical proper-ties. The substances with which we are dealing should not all be classed as proteins. The muco-polysaccharides of our terminology were formerly included as mucins and as mucoids in the group of conjugated proteins. They occur in nature either as free polysaccharides or as protein salts. The second group, the glycoproteins, are polypep-tides to which a neutral hexosamine-containing polysaccharide appears to be firmly bound. In bacteria both classes are apparently present, but there remains much to be done in the characteri-zation of definite chemical fractions. A logical classification of the hexosamine-con-taining compounds should be based on the nature of the carbohydrate radical, since the latter is most easily determined. Table I shows the classifica-tion which we propose.