Mucoprotein

A Crystalline Serum Mucoprotein with High Cholinesterase Activity, R. Bader, F. Schultz, and M. Stacey,Nature, 154(1944) 183-184. 

Unit of chitin, mucoproteins and mucopolysaccharids, obtained by hydrolysis with HCI. 

Lipoproteins. The lipid moiety of the lipoproteins is quite variable, both qualitatively and quantitatively Mucoproteins are carbohydrate in nature Chromoproteins are pigments... 

In this classification of the compounds into mucopolysaccharides, mucoproteins, and mucolipids, it must be emphasized most strongly that since the mode of isolation of any naturally occurring high polymer influences profoundly its composition and biological properties, the difference between divisions is not always sharp and there may be some degree of overlapping. 

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 mechanism of the conversion of cellulose by the Cytophagaem into viscous mucoproteins of high molecular weight forms an unexplored subject of great interest. 

Since antibodies occur in the globulin fraction of serum one predicts that the investigation of the fine structure of serum mucoproteins will become a problem of urgent immunological significance. It is doubtful however whether the carbohydrate group of mucoproteins can influence their immunological specificity.1 ... 

The physiological significance of mucoproteins in serum is unknown but it is tempting to speculate that they may simply be intermediate stages in the synthesis of albumins and globulins. However, it will be seen below that mucoproteins with hormone properties can be isolated from serum of pregnant mares, and that the enzyme choline esterase, is probably a serum mucoprotein. 

Rimington and Rowlands165 have isolated an extremely active preparation from the serum of pregnant mares. This material was obtained in a high degree of purity and was shown to contain hexose and hexosamine in the molar ratio of 2/1. In the fractionation it appeared that, at first, the hexose content decreases as the potency is raised, but later this trend is reversed. It was shown that hexose content could not be taken as indication of gonadotropic activity. The hexose/hexosamine ratio was 2/1 as in normal serum mucoproteins, so that this gonadotropic hormone may be a modified serum mucoprotein. 

By a careful fractionation of normal horse serum, involving as an essential part of the process a separation of closely related substances by the Schtitz168 foam technique, Bader, Schiitz and Stacey16 obtained a crystalline mucoprotein with high choline esterase activity. This appears to be the first mucoprotein obtained without the use of heat or alcohol, and while it is not yet claimed that the crystalline material is indeed the enzyme itself, arguments are advanced to show that the enzymic activity is closely bound up with mucoprotein structure. 

The vague definition offered above or rather these characteristics appear to be sufficient since no plasma protein capable of forming a strong bond with Hb is known to occur in mammalian plasma except those mucoproteins with the general biochemical properties originally accepted as characteristic of haptoglobins. 

The mucoprotein nature of Hp was soon recognized by Jayle. The polysaccharide part comprised 22% of the molecule according to Cheftel et al. (Cl) and 18.5 according to Schultze and Heide (S2). 

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