General Properties of Saliva Proteins 171 



sion that molecules having these properties have a voluminous 

 random coil structure within which large volumes of solvent are 

 trapped, this is in contrast to the more compact hydrogen bonded 

 structure characteristic for ordinary proteins in solution. Presum- 

 ably submaxillary and other viscous salivas contain mucoproteins 

 with molecular configurations similar to those found in hyaluro- 

 nate, whereas in the mucoproteins of non-viscous saliva the intra- 

 molecular structure is determined more by the peptide framework 

 than by long freely coiling polysaccharide chains. 



The property of forming a ' 'mucin clot" with dilute acid appears 

 to be restricted to acidic mucoproteins, i.e. those with free carboxyl 

 groups of uronic acids or sulphato groups of sulphohexosamine. 

 While the free polysaccharide may show this reaction in dilute 

 solution it usually needs the presence of proteins such as serum 

 albumin for an insoluble complex to form. The nature of the pre- 

 cipitate is quite dependent on the character of this adsorbed pro- 

 tein. For instance, hyaluronate forms a stringy clot in the presence 

 of native albumin, but a flocculent precipitate in the presence of 

 partly proteolysed albumin. Komarov and Stavraky (1940) noted 

 that the saliva produced by sympathetic stimulation of the cat 

 submaxillary gland gave a flocculent precipitate with acid acetone, 

 whereas chorda saliva from the same gland precipitated as compact 

 viscous masses. While part of this difference is probably due to 

 intrinsic differences in the protein secreted coprecipitation effects 

 may also be involved. 



The multicomponent nature of saliva proteins has been demon- 

 strated by electrophoresis, ultracentrifugation and immunological 

 methods (Blix, 1940; Patton, 1956; Patton and Pigman, 1957, 

 1959; Kostlin and Rauch, 1957; Ferguson, Krahn and Hildes, 

 1958; Ellison and Mashimo, 1958; Motta and Motta, 1958; Gabl 

 and Egger, 1959). In the best of the electrophoretic studies 5-9 

 distinct components were found which differ in submaxillary and 

 parotid saliva (Figs. 9. 1 and 9.2). In human parotid saliva the major 

 peak has been identified as amylase (which is not present in all 

 parotid salivas; v. infra). In submaxillary saliva the major com- 

 ponent is a mucroprotein of low mobility, presumably a neutral 

 mucoprotein, but carbohydrate-rich fractions of high mobility 

 (acidic mucoproteins) are also present. In the ultracentrifuge, paro- 

 tid saliva shows 4 components (i-i, 2-0, 4-2 and 107— Svedberg 

 units) and submaxillary saliva 3 components (1-3, 4-1 and u-o 



