The purification and partial amino acid sequence of a polypeptide from the glutelin fraction of rice grains; homology to pea legumin

The glutelin fraction was extracted from grain meals of rice (Oryzea sativa) with 50 mM Tris‐HCl buffer (pH 8.8) containing 6 M urea and 10 mM 2‐mercaptoethanol. Polypeptides of glutelin were separated and purified by ion‐exchange chromatography under denaturing conditions. Analysis by two‐dimensional gel electrophoresis showed that 2 major polypeptides of the rice glutelin fraction, M r 36 000 and 22 000, were linked in disulphide bonded pairs containing one M r 36 000 and one M r 22 000 subunit. A partial amino acid sequence of the purified M r 22 000 glutelin subunit showed it to be homologous to the β‐subunit of pea legumin, a storage protein which also contains disulphide‐linked subunit pairs (M r 38 000 and M r 22 000). It is therefore proposed that the major component of rice glutelin is a legumin‐like protein.