ISOLATION, CHARACTERIZATION, AND SUGAR CHAIN STRUCTURE OF ENDOPG IA, IB, AND IC FROM STEREUM-PURPUREUM

Three endopolygalacturonases (endoPG Ia, Ib, and Ic) were isolated fro m the culture filtrate of Stereum purpureum, the causative fungus of a pple silver-leaf disease. Their properties, including specific activit ies, optimum pHs, thermal stabilities, and kinetic parameters (K-m and V-max) were compared. Their properties were very similar to one anoth er except for the substrate specificity and relative molecular mass. T he sugar chains of endoPG Is were released by hydrazinolysis, and one major sugar chain common to endoPG Is was isolated. The pyridylamino s ugar was characterized by a two-dimensional mapping method using HPLC, and identified as a high mannose type N-linked sugar chain, Man alpha 1-6(Man alpha 1-3)Man alpha 1-6(Man alpha 1-3) Man beta 1-4GlcNAc bet a 1-4 GlcNAc (designated as M5.1). Observation of the course of Wester n blot analysis for the proteins from the culture filtrate with endoPG I antibodies showed that the fungus secreted three endoPG Is into the culture broth during the growing period.