Isolation and Characterization of Arabinogalactan Proteins Released by Cellulase Digestion of Cabbage Leaves

A new type of arabinogalactan protein (AGP) tightly associated with cellulose microfibrils and pectic substances was found to be released by cellulase digestion of the insoluble residues given from cabbage leaves after extractions with water and hot water. The content of AGPs in head leaves of cabbage was 2.5-fold higher than that of green leaves. These AGPs were fractionated into five components (C-II 1 -C-II 5 ) by combination of gel filtration on Sepharose CL-4B and ion-exchange chromatography on DEAE-Toyopearl. The C-II 1 fraction eluted from a DEAE-Toyopearl column at 0.07 M NaCl was a typical AGP which is rich in hydroxyproline (28.3%) and consists of protein (15.4%), neutral sugar (78.8%) with an arabinose/galactose ratio of 1.6 :1, and uronic acid (5.8%). The chemical composition analysis of the other four glycoproteins (C-II 2 -C-II 5 ) eluted at 0.15, 0.175, 0.2, and 0.3 M NaCl, respectively, indicates that these AGPs were complexed with rhamnogalacturonan having wide spectra in protein and pectin contents. The present results furnish AGPs with the structural functions of the primary cell wall in cabbage leaves.