Complete amino acid sequence of luffin-a, a ribosome-inactivating protein from the seeds of sponge gourd (Luffa cylindrica).

The complete amino acid sequence of luffin-a has been determined. Twenty-two peptides were isolated from the tryptic digest of luffin-a and sequenced employing the DABITC/PITC double coupling method. Overlaping of these peptides was achieved by analyzing the chymotryptic peptides or CNBr-fragments of luffin-a and their S. aureus V8 protease peptides. Luffin-a consists of 248 amino acid residues and its relative molecular mass is calculated to be 27,021 Da, excluding the attached sugar chains reasoned to be present at each Asn residue of positions 28, 33, 77, 84, 206, and 227. A comparison with the sequence of ricin A-chain showed 33% sequence identity indicating that these proteins are homologous.