ASPARAGINE-LINKED CARBOHYDRATE CHAINS OF INDUCIBLE RAT PAROTID PROLINE-RICH GLYCOPROTEIN CONTAIN TERMINAL BETA-LINKED N-ACETYLGALACTOSAMINE

Rats treated with daily injection of DL-isoproterenol for 10 consecuti ve days (25 mgkg(-1) body weight) showed marked induction of a proline -rich glycoprotein (GPRP) of 220 kDa. Proteinase K digestion of GPRP p roduced a homogeneous glycopeptide with an average chemical compositio n as follows (residues per mol): Pro(4), Glx(3), Asx(2), Gly(1), His(1 ), Thr(1), Arg(1), GlcNAc(5), GalNac(1), Man(3), Gal(2-3), and Fuc(1). The structural analysis of the asparagine-linked carbohydrate unit wa s performed by methylation, periodate oxidation and enzymatic degradat ion. Methylation studies indicated that the three mannosyl residues we re substituted at 1,2-, 1,2,4-, and 1,3,6-positions. Fucose, N-acetylg alactosamine, 1.5 residues of galactose and 0.35 residues of N-acetylg lucosamine were terminally located and one galactose residue was 1,4-s ubstituted. Approximately four of the 5 N-acetylglucosamine residues w ere substituted at 1,4-position and approximately 1 residue of N-acety lglucosamine was substituted at 1,4,6-positions. Periodate oxidation s tudies and exoglycosidase results were consistent with the methylation data. Based on the results of Smith degradation, methylation and sequ ential exoglycosidase digestions a triantennary oligosaccharide struct ure having terminal N-acetylgalactosamine in one of the branches is pr oposed for the major Asn-linked carbohydrate moiety of GPRP.