Morphology, Associated Protein Analysis, and Identification of 58-kDa Starch Synthase in Mungbean (Vigna radiata L. cv. KPS1) Starch Granule Preparations

Raw starch granules of mature mungbean (Vigna radiata L. cv. KPS1) seeds were prepared by two methods into crude and cesium chloride (CsCl)-washed forms. The purity, shape, size distribution, and associated protein profiles were examined. The appearance of raw starch granules showed a bimodal type distribution in which average granules had typical ovoid shapes, whereas the small ones were spherical. Abnormal granule surface with distinct tumor-like or dented hole features were also observed in raw starch granules. CsCl-washed granules had a smooth surface compared to that of the crude form. The granule size distribution ranged from 6-35 mu m; most 15-25 mu m (similar to 53%), followed by 25-35 mu m (similar to 26%). Small granules (<15 mu m) amounted to similar to 18%, and granules >35 mu m consisted of similar to 3%. The two forms were further refined by trichloroacetic (TCA) treatment to reveal surface proteins on the crude granules or tightly bound proteins on CsCl-washed granules. In the washed-refined granules, only a few integral proteins were retained. The major 58-kDa protein was identified to be granule-bound starch synthase I by sequence homology with that in cowpea (Vigna unguiculata) and maize (Zea mays) using MALDI-TOF mass and Mascot search.