Structural study on arabinogalactan–proteins from Picea abies L. Karst

Two homogeneous arabinogalactan–proteins (AGPs) have been purified from spruce (Picea abies L. Karst) callus cells by ion-exchange and gel-permeation chromatography, followed by enzymic treatment. The apparent molecular masses of these highly glycosylated proteoglycans AGP-1 and AGP-2 were 43 and 19 kDa, respectively. Both macromolecules contained predominantly terminal α-l-arabinofuranosyl residues, terminal, 3-, 6-, and 3,6-linked β-d-galactopyranosyl residues, and terminal β-d-glucopyranosyluronic acid residues. The presence of a pyruvate substituent on O-4,6 of some of the 3-linked β-d-galactopyranosyl residues was proved for both AGPs. The protein moiety was rich in hydroxyproline, serine, threonine, and alanine. Reductive alkaline degradation of the AGPs indicated that serine and threonine were not involved in the carbohydrate–protein linkage. While sharing general structural similarity, these endoplasmic AGPs were distinguishable by composition, size, and shape of the macromolecules.