OCCURRENCE OF A SIALYLGLYCOPEPTIDE AND FREE SIALYLGLYCANS IN HENS EGG-YOLK

Free sialylglycans (FSGs) and a sialylglycopeptide (SGP) as components of hen's egg yolk were found and their chemical structures were deter mined. SGP and FSGs were isolated from fresh egg yolk by treatment wit h phenol, gel filtration and successive chromatographies on columns of anion- and cation-exchangers. They were localized in the yolk plasma. The glycan moiety of SGP, which was liberated by PNGase digestion, wa s studied for the chemical structure by HPLC mapping with p-aminobenzo ic ethylester-derivatization, sugar composition analysis, H-1 nuclear magnetic resonance and matrix-assisted laser desorption/ionization tim e-of-flight (MALDI-TOF) mass spectrometry and the glycomoiety was foun d to be an N-linked disialyl-biantennary glycan. The amino acid sequen ce of the peptide moiety of SGP was determined to consist of Lys-Val-A la-Asn-Lys-Thr, the Asn of which is modified with the disialylglycan m oiety. FSGs were determined to be two free disialyl-biantennary glycan s whose reducing end was either drop Man beta 1-4GlcNAc (FSG-I) or dro p Man beta 1-4GlcNAc beta 1-4G1cNAc (FSG-II). Since the molar value of SGP present in one egg yolk (2.8 mu mol) is comparable to those of we ll-known major yolk proteins, low density lipoprotein, lipovitellins a nd phosvitin, it can be considered that SGP is one of the major compon ents in hen's egg yolk.