Studies on the Mucoproteins of Human Plasma

The presence in plasma of protein-like materials with properties of polypeptides or proteoses has been demonstrated repeatedly, but little has been done toward the characterization of these materials. The concentration of such materials in plasma rises markedly in patients with cancer or with certain other diseases, but here again little is known of the source or significance of the increased levels. The relation of these protein-like materials to the glycoproteins and mucoproteins of plasma is likewise in a state of considerable confusion. The present series of experiments has grown out of three distinct avenues of attack (a) the demonstration, polarographically, of high molecular weight compounds containing cystine in sulfosalicylic acid filtrates of serum (1 to 6), (b) the demonstration of polypeptide-like substances in serum deproteinated with trichloracetic acid (7 to 10), and (c) the demonstration of a carbohydraterich protein, seromucoid, present in filtrates of serum deproteinated by heat (11 to 14). It appears very likely that these materials are identical, and for reasons that will be developed in this paper, the materials will be referred to as mucoproteins. Winzler and Burk (6) isolated the non-dialyzable material from sulfosalicylic acid filtrates of rat blood, and compared the properties and occurrence of this material with the older studies of plasma polypeptides. They concluded that the isolated product was identical with the substances