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The Metabolism of Plasma Glycoproteins

II. Studies on the Rate of Incorporation of Glucosamine-1-¹⁴C into Protein-bound Hexosamine in the Rat Bearing Walker 256 Carcinoma¹

Department of Surgery and the Surgical-Medical Research Institute, University of Alberta, Edmonton, Alberta, Canada

The origin of the elevated serum glycoproteins observed in rats bearing 6- and 12-day-old Walker 256 carcinoma has been studied utilizing glucosamine-1-¹⁴C as a precursor. The results indicate that the liver is quantitatively the major site of serum glycoprotein biosynthesis as is the case in the normal animal. While the rate of incorporation of glucosamine-1-¹⁴C into hepatic protein-bound hexosamine was not altered from normal in the early stages of tumor development, the 12-day-old Walker carcinoma provoked a significant increase in the hepatic binding of glucosamine-1-¹⁴C. In both tumor age groups the biologic half-life of the hepatic protein-bound hexosamine was longer than in normal animals.

In vivo studies following hepatectomy, with and without isolation of the tumor, and in vitro studies would strongly suggest that the tumor too is metabolically active with respect to glycoprotein biosynthesis and release. Furthermore, the rate of synthesis appears to depend on the volume of viable tumor rather than its age.

Evidence is presented which indicates that, in tumor bearing rats, the biosynthesis of the seromucoid fraction is significantly increased. In tumor bearing rats seromucoid synthesis represents 23–27% of the total serum glycoprotein synthesized as compared with a figure of 8.9% for normal animals. The biologic half-life of both the total serum glycoprotein and the seromucoid fraction is, however, significantly shorter in tumor bearing than it is in normal rats.

Analysis of the urine in both tumor age groups revealed that over 90% of the radioactivity that was recoverable in the urine was associated with free glycosamine and other as yet uncharacterized compounds.

The incorporation of administered glucosamine-1-¹⁴C into body tissues, other than liver and tumor, was minimal in comparison.

¹ This work was supported by Grant 226 from the National Cancer Institute of Canada.

² Present address: Department of Biochemistry, State University of New York, Buffalo, New York.

Received 2/ 2/66. Accepted 5/25/66.