Isolation and Molecular Characterization of Four Arginine/Glutamate Rich Polypeptides from the Seeds of Sponge Gourd (Luffa cylindrica)

Abstract

Four arginine/glutamate rich polypeptides referred to as 5k-, 6.5k-, 12.5k-, and 14k-AGRPs were purified to homogeneity by gel filtration on Sephadex G-75 followed by CM-cellulose, butyl-Toyopearl 650M, and reverse-phase HPLC from the seed of sponge gourd (Luffa cylindrica). Tricine SDS-PAGE indicated that 5k-and 6.5k-AGRPs are single polypeptides, but 12.5k- and 14k-AGRPs consist of two polypeptide chains which are linked by disulfide bond(s). The N-terminal amino acid sequences of four AGRPs were analyzed by a gas-phase sequencer, and the result indicated that they are distinct molecules. Comparison of the sequences with those of proteins in the protein data base demonstrates that 5k- and 6.5k-AGRPs have a significant homology with a basic peptide from pumpkin seeds and with cocoa seed vicilin, respectively, and that 12.5k- and 14k-AGRPs are related to 2S seed storage proteins. Furthermore, it was assumed that the four AGRPs might occur in the protein bodies within cells of the seed.