Hexosamine containing compounds

A similarity of leucodystrophy to some of the classic lipidoses was pointed out by Edgar (1955,1957) who had found increases of hexosamine-containing compounds in nine cases. On the basis of this finding ML was defined as a special type of degenerative diffuse sclerosis (Hallervorden 1957). 

Compounds of this type were first classified by Meyer (262, 263) who, however, included only hexosamine-containing compounds. Stacey (408, 409) proposed a classification which included many additional complex carbohydrates and some of the bacterial polysaccharides that are discussed later. 

Glycoproteins or mucoproieins. Compounds of proteins with carbohydrates. All glycoproteins contain a hexosamine and usually sulphate, ethanoate and glucuronic acid. The carbohydrate-protein linkages are, in some cases covalent and in others of the salt type. Aqueous solutions of glycoproteins are extremely viscous. 

Mucoproteins (See Section V).—Protein-carbohydrate compounds with relatively high protein or peptide content, the chemical reactions of which are predominantly protein, are known as mucoproteins. In general they do not coagulate on being heated in aqueous solution. All mucoproteins contain a hexosamine constituent. 

The list of compounds given in Table 7.13.1 contain some long chain fatty acids (tetradecanoic acid, pentadecanoic acid, hexadecanoic acid) that probably are not generated from chitin itself but from associated materials present in the chitin sample (chitin purification is difficult due to its insolubility). The main pyrolysis mechanism seems to be similar to that of cellulose. 1,6-Anhydro-2-acetamido-2-deoxyglucose seems to be a major component in the pyrolysate as are further dehydrated hexosamines. 

A number of biologically important compounds or complexes of carbohydrates with lipides and sometimes also with proteins have been found in animal tissues (and some bacteria). The Wassermann antigens and the Forssman antigens apparently are materials of this type. The cerebrosides and gangliosides (Chapter X) might be considered to belong to this group. All appear to contain a hexosamine residue. 

These are protein-carbohydrate compounds which contain 10-75% of carbohydrate and over 4% of hexosamines (as distinct from glycoproteins which contain from a trace up to 15% carbohydrate and less than 4% of hexosamines). Oroso-mucoid, haptoglobin and haemopexin are examples of muco-proteins. Increased serum mucoprotein levels are found in many inflammatory conditions such as acute infections and rheumatoid arthritis. Mucoproteins can be estimated by selective precipitation using phosphotungstic acid, followed by determination of the protein or carbohydrate content of the precipitate. 

Heparin resembles chondroitinsulfuric acid and mucoitinsulfuric acid in that it is composed of glucuronic acid (449), a hexosamine (in this case glucosamine), and contains sulfate groups. Most investigators also report the presence of acetyl groups as in the case of chondroitin- and mucoitinsulfuric acids, but Wolfrom s analyses (452) of heparin did not reveal their presence. As with these related compounds, the structure of heparin has... 

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