Properties and subunit characterization of affinity purified Sophora japonica lectin

The affinity purified Sophora japonica lectin exhibits an anomalous behavior on polyacrylamide gel electrophoresis (PAGE). Electrophoresis at pH 8.9 produces three protein staining bands. Extraction and re-electrophoresis of the fastest and slowest migrating components demonstrates that the lectin solution is an equilibrium mixture of interconvertible forms. Addition of a bindable saccharide, D-galactose, during PAGE causes the equilibrium to be shifted toward a single form. As indicated by analytical gel filtration, sedimentation velocity ultracentrifugation and ion-exchange chromatography experiments, the equilibrium mixture consists of charge and not molecular weight variants of the native molecule of 132,800 g/m. Results from end-group and cysteine analyses and PAGE in sodium dodecyl sulfate indicate that the native lectin is composed of the non-covalent association of two dissimilar subunits. One subunit consists of two identical polypeptide chains attached by two disulfide bonds and the other subunit of two identical polypeptide chains stabilized by a single cysteine bridge.