Structure of Glycopeptides Isolated from Bovine Milk Component PP3

The heat‐stable acid‐soluble phosphoglycoprotein component PP3 was isolated from the bovine milk proteose peptone fraction by concanavalin A affinity chromatography. Glycopeptides were released by pronase digestion of the milk component PP3 and were subsequently separated by high‐pH anion‐ex‐change chromatography on Carbopac PA‐1. The primary structures of the glycan and peptide moieties of eight N‐glycopeptides have been established by combining methylation analysis, mass spectrometry, 400‐MHz 1H‐NMR spectroscopy, and peptide sequence analysis. All the analyzed fractions contained biantennary N‐acetyllactosamine‐type carbohydrate chains, some of them with a GalNAc(β1–4)GlcNAc or a NeuAc(α2–6)GalNAc(β1–4)GlcNAc group. This particular sequence did or did not replace the Gal(β–4)GlcNAc group usually found in most N‐linked glycans. Moreover, the sialylated Gal and GalNAc residues were only found on the Man(α1–3) antenna.