BIOSYNTHESIS OF PROTEOGLYCOGEN - MODULATION OF GLYCOGENIN EXPRESSION IN THE DEVELOPING CHICKEN

Glycogenin, the autoglucosyltransferase that primes the biosynthesis o f proteoglycogen, is found in the polysaccharide Linked proteoglycogen form in mammals and chicken. Glycogenin was released from proteoglyco gen and its activity was measured, together with that of glycogen synt hase as well as glycogen content, in muscle, liver, and brain during c hicken development. The specific activity of glycogenin, expressed per protein, increased with development only in muscle and was higher tha n the specific activities measured in Liver and brain at any time. Con comitant with the rise in activity, an enhanced expression of the prot ein was observed with Western blot. The specific activity of glycogen synthase increased with development in muscle and liver, while glycoge n accumulation was noticeable only in liver. The results indicate that the molar concentration of proteoglycogen is higher in muscle than in liver, The high glycogen content of Liver may indicate that the size of the polysaccharide moiety of proteoglycogen is larger in Liver than in muscle. This is the first report of developmental modulation of de novo biosynthesis of glycogen at the level of the primer that initiat es glucose polymerization. (C) 1997 Academic Press.