ISOLATION AND PROPERTIES OF A SIALOGLYCOPROTEIN FROM THE SKIN MUCUS OF THE STINGRAY DASYATIS-AKAJEI

A sialoglycoprotein (SGP) has been purified from the skin mucus of the stingray Dasyatis akajei. SGP contained 22.1% (w/w) NeuAc, 24.4% GalN Ac, 9.9% GlcNAc, 6.1% Gal, and 27% amino acids, and its average molecu lar weight (Mr) was estimated to be 500,000. SGP was very rich in Thr (32 mol%) and Ser (12 mol%). Treatment of SGP with alkali (beta-elimin ation of carbohydrate chains) resulted in the destruction of 70% of Th r and Ser, indicating that the carbohydrate chains were attached throu gh these amino acids. Exhaustive digestion of SGP by actinase yielded a highly glycosylated glycopeptide with Mr of 50,000. Based on these r esults, it is assumed that a SGP molecule bears more than 400 oligosac charide chains which are attached to the Thr and Ser residues of the p olypeptide backbone and spaced at an average of 3 amino acids apart.