PRIMARY STRUCTURE OF 6.5K-ARGININE GLUTAMATE-RICH POLYPEPTIDE FROM THE SEEDS OF SPONGE GOURD (LUFFA-CYLINDRICA)/

The amino acid sequence of 6.5k-arginine/glutamate rich polypeptide (6 .5k-AGRP) from the seeds of sponge gourd (Luffa cylindrica) has been d etermined, The 6.5k-AGRP consists of a 47-residue polypeptide chain co ntaining two disulfide bonds, and a molecular mass calculated to be 56 95 Da, which fully coincides with a value of [M + H](+) = m/z 5693.39 obtained by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS), The mass spectrometric evidence ind icated that 6.5k-AGRP is also present partially truncated at the C-ter minus, In our preparations, approximately half of the polypeptide mole cules have the C-terminal sequence Arg-Arg-Glu-Val-Asp; the other half lack Val-Asp and end with the glutamic acid, making a total of 45 res idues in the polypeptide chain, The two disulfide bonds connect Cys(12 ) to Cys(33) and Cys(16) to Cys(29), Comparison of the amino acid sequ ence of 6.5k-AGRP with those of the other known proteins included in t he PIR protein sequence database showed that it is related to the amin o acid sequence of the N-terminal region encoded by the first exon of the cocoa (Theobroma cacao) and cotton seeds vicilin genes, sharing a characteristic two Cys-Xaa-Xaa-Xaa-Cys motif.