Studies on the biosynthesis of glucosamine in the intact rat.

Little is known about the biosynthesis of glucosamine in mammalian organisms. Previous studies have indicated the presence of enzymes in several mammalian tissues capable of synthesizing glucosamine (1, 2). Moreover, there is evidence that glucose, without scission of its carbon chain, may serve as the precursor of glucosamine in the intact animal (3, 4), as in bacteria (5, 6). However, except for studies on the mucopolysaccharides of skin (7, 8), no information is available on the rate of turnover of glucosamine in mammalian tissues. It would be of special interest to have information concerning the rate of turnover and the site of synthesis of the serum glucosamine, which is present in large concentrations and is apparently entirely proteinbound. As a major carbohydrate component of the serum glycoproteins, it undergoes wide fluctuations in concentration in a variety of physiological and pathological states (9). In the present study a comparison was made of the incorporation of radioactivity from glucose-C14 into the protein-bound glucosamine of various tissues of the intact rat. Of the tissues studied, liver and serum showed the most rapid synthesis of glucosamine from glucose, and a detailed analysis of the turnover of glucosamine in both of these tissues was made. Evidence is also presented that the liver is the primary site of synthesis of the serum glucosamine.