Properties and Subunit Characterization of Affinity Purified Sophora Japonica Lectin

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Abstract
Affinity purified S. japonica lectin exhibits an anomalous behavior on polyacrylamide gel electrophoresis (PAGE). Electrophoresis at pH 8.9 produces 3 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 MW 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 noncovalent association of 2 dissimilar subunits. One subunit consists of 2 identical polypeptide chains attached by 2 disulfide bonds, and the other subunit of 2 identical polypeptide chains stabilized by a single cysteine bridge.