Amino acid sequence of small and large subunits of seed storage protein from Ricinus communis

The low molecular weight, glutamine-rich storage protein isolated from the seeds of Ricinus communis (castor beans) has been shown to consist of two different polypeptide chains linked by disulfide bond(s). The small subunit is composed of 34 amino acids with a proline at its NH2 terminus, whereas the large subunit contains 61 amino acids with a cyclized glutamine as the NH2-terminal residue. The complete amino acid sequence of both subunits has been determined through characterization of the isolated subunits and selected peptides from trypsin, chymotrypsin, thermolysin, and cyanogen bromide cleavage. The intact protein possesses a large number of glutaminyl and half-cystinyl residues and exhibits sequence heterogeneity as observed from peptide sequences. Comparison of the sequence of this protein and those of other seed proteins indicates some structural similarities between them. The amino acid sequences of the two polypeptide chains of castor bean storage protein are: (formula, see text).