Incorporation of D-[1-14C]galactosamine into serum proteins and tissues of the rat

Incorporation of D-[1-¹⁴C]galactosamine into serum proteins and tissues of the rat was studied. After single intraperitoneal injections, about 20% of administered radioactivity was excreted in urine within 6 h. Only 1% was found in expired CO₂ at this time; 12% was found at 72 h. High levels of bound (non-dialyzable) radioactivity appeared first in liver and then in serum. Non-dialyzable radioactivity in serum was found associated with all electrophoretically separated fractions with the greatest concentration in the α-globulins. Hexosamines were separated by paper chromatography from serum protein hydrolysates; glucosamine had a ¹⁴C content over ten times that of galactosamine in a sample taken 6 h after injection. A progressive increase in non-dialyzable radioactivity with time was found in both connective tissue and the fluid from within stainless-steel wire mesh cylinders implanted subcutaneously 2 weeks prior to injection of [1-¹⁴C]galactosamine. Mucopolysaccharides, extracted from connective tissue, exhibited electrophoretic mobility and staining characteristic of chondroitin sulfate and hyaluronic acid. Although hyaluronic acid and chondroitin sulfate moieties were labeled to the same extent, their hydrolysates contained glucosamine with 4 times more radioactivity then galactosamine, possibly indicating the presence of a substance containing glucosamine in the chondroitin sulfate area. These results indicate that much of the galactosamine is converted to glucosamine. Radioactive galactosamine appears to be of value for metabolic studies of glycoproteins and mucopolysaccharides.