Identification of an endogenous Con A-binding polypeptide as the heavy subunit of α-mannosidase

Abstract

We showed in [l] that the specificity of endogenous lectins for glycoproteins in homologous plant species was extremely high. In jackbean cotyledons, a major polypeptide recognised by concanavalin A (Con A) had an Mr app. z 68 000 and could be purified from an aqueous-buffered extract by affinity chromatography on immobilised Con A. When we assayed glycosidase activities in extracts of cotyledons and embryonic axes, we found that the only glycosidase with significantly different activity in the 2 tissues was a-mannosidase [2,3]. cu-Mannosidase activity was extremely high in the cotyledon extract and virtually absent from the axis extract. This tissue distribution paralleled that of the endogenous lectin Con A [ 1,3] and suggested the possibility that the 2 seed components were in some way related. Here, we suggest that the major Con A binding polypeptide in jackbean cotyledons is the heavy subunit of a-mannosidase.