Identification of a starch-branching enzyme and coexisting starch biosynthetic enzymes from partially purified mung bean (Vigna radiata L.) fractions

Three starch-branching enzyme (BE) bands (I, II and III) were detected by zymogram in the soluble extract of developing mung bean (Vigna radiata L. cv KPS1), and radioactive method was used to trace BE during purification by liquid chromatography. Protein profiles of bands I and II were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and identified by proteomic analysis with liquid chromatography-mass spectroscopy/mass spectrometry and bioinformatic searching. The 96 kDa BE possessing specific amino acid sequences of the A-type family of BEs was identified from band II. Mung bean 92 kDa sucrose synthase and the previously identified 105 kDa starch phosphorylase (SP) and its 55 kDa fragments were also found in both bands I and II. Western blotting with SP antibodies showed that SP was present in all of the purified BE fractions. In summary, with the aid of proteomic analysis, we have identified a major mung bean BE and coexisting starch biosynthetic enzymes from partially purified fractions.