Mucoproteins proteins, nature

The term microbial toxin is usually reserved by microbiologists for toxic substances produced by microorganisms that are of high molecular weight and have antigenic properties toxic compounds produced by bacteria that do not fit these criteria are referred to simply as poisons. Many of the former are proteins or mucoproteins and may have a variety of enzymatic properties. They include some of the most toxic substances known, such as tetanus toxin, botulinus toxin, and diphtheria toxin. Bacterial toxins may be extremely toxic to mammals and may affect a variety of organ systems, including the nervous system and the cardiovascular system. A detailed account of their chemical nature and mode of action is beyond the scope of this volume. 

It is of interest that a nonulosaminic acid is found in all the mucoprotein inhibitors so far tested and also in a mucoprotein present in erythrocytes/ - although it is not yet clear what other chemical and physical relationships may exist between the alternative viral substrates, the inhibitors, and the natural, cell receptors. No quantitative relationship has been noted between the capacity to inhibit hemagglutination and the content of nonulosaminic acid in the individual, inhibitory sialoproteins. The possible role of a polypeptide or protein moiety in conferring the inhibitory properties is suggested by the observation that a mucolipid fraction (from ox brain), which contains both a peptide and a nonulosaminic acid, will inhibit viral hemagglutination. Destruction of the peptide component by tryptic digestion results in loss of the inhibitory function. 

After precipitation of serum protein with sulfosalicylic acid, the filtrate contains proteins not precipitable with the reagent which have the nature of mucoproteins or glucoproteins. The filtrate consequently also yields a typical protein double wave. The polarographic behavior of mucoproteins is essentially analogous to that of other proteins. This filtrate reaction is so intimately connected with the applications that a division of its discussion between two chapters would be devoid of logic and sense. For this reason it is discussed in Section III, chapter 8. 

Masamune and associates (4) have provided some information concerning the nature of the combinations in other types of mucoproteins and of the proteins in the combinations. The mucoproteins of cartilage (chondro-mucoid) and of umbilical cord (funis mucin), removed from the tissues by aqueous extraction, are precipitated at pH 2 to 3. When the precipitated mucoproteins were extracted with solutions over the range pH 1 to 4, the composition of the residue did not remain constant evidently the ratios of protein to carbohydrate in the mucoproteins are dependent upon the pH. Tendomucoid (from tendon) and osseomucoid (from bones) appear to be similar if not identical to chondromucoid. 

The nature of the proteins involved in mucoproteins and glycoproteins has received some preliminary study (4, 71), A slight amount of evidence exists that the common protein components are albumins and globulins, except in mucous secretions. Pepsin and trypsin hydrolyze many of the mucoproteins or glycoproteins, but salivary mucoid and ovomucoid are quite resistant. At physiological pH (7.25 to 7.30), only fairly basic proteins would be expected to bond with carboxyl groups, and the sulfate bonding would be most probable for the common proteins. 

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