THE COMPLETE AMINO-ACID-SEQUENCE OF MOMORDIN-A, A RIBOSOME-INACTIVATING PROTEIN FROM THE SEEDS OF BITTER GOURD (MOMORDICA-CHARANTIA)

The complete amino acid sequence of momordin-a, a ribosome-inactivatin g protein from the seeds of bitter gourd, has been analyzed. Twenty-tw o peptides were isolated from the tryptic digest of momordin-a and seq uenced by the DABITC/PITC double coupling method. The alignment of the se tryptic peptides was done by analyzing the amino acid sequences of the peptides derived from chymotryptic digestion and cyanogen bromide cleavage of momordin-a as well as V8 protease-digestion of the CNBr fr agment. Momordin-a consisted of 250 amino acid residues and carbohydra te residues attached to Asn227, and its molecular mass was calculated to be 28,690 Da. The sequence comparison with ricin A-chain shows that 33% of the residues of momordin-a are identical to those of ricin A-c hain and that the residues involved in the catalytic site of the ricin A-chain are conserved in momordin-a.