Polyamine synthesis in plants. Purification and properties of amidinotransferase from soybean (Glycine max) axes

Abstract Three-day-old soybean ( Glycine max ) seedlings were exposed to 0.4 M sorbitol solution for 4 h to induce amidinotransferase activity, with the corresponding enzyme being purified to homogeneity by chromatographic separation on DEAE-Sephacel, Sephacryl S-300 and l -arginine Sepharose 4B. The purified enzyme used l -arginine and l -glycine as the major donor/acceptor of the amidino group, respectively, with formation of guanidinoacetic acid and ornithine products being confirmed by ESI-MS. The enzyme is a tetrameric protein having a molecular mass of 240,000 Da, whose thiol group is needed for enzymatic activity. The K M s for arginine and glycine were 3.8 and 0.89 mM, respectively, with optimal temperature and pH being 37 °C and 9.5, respectively. The soybean amidinotransferase could be indirectly involved in nitrogen metabolism, as suggested by the observation that arginine:glycine amidinotransferase in soybean axes is indirectly involved in putrescine biosynthesis and displays feedback control at high levels of an endogenous regulator, putrescine.