Isolation and amino acid sequences of two trypsin inhibitors from the seeds of bitter gourd (Momordica charantia).

Abstract

Two novel trypsin inhibitors, MCTI-II' and BGIT, were isolated from the seeds of bitter gourd (Momordica charantia) and their amino acids sequenced. MCTI-II' was a squash type trypsin inhibitor and lacked the N-terminal arginine residue of Momordica charantia trypsin inhibitor (MCTI)-II. It consists of 27 amino acid residues and forms a dimeric structure. BGIT had 88% homology with bitter gourd inhibitor against an acidic amino acid-specific endopeptidase (BGIA) consisting of 68 amino acid residues and inhibited not only trypsin but also subtilisin Carlsberg. The amino acid replacements occurred in 8 positions of which that of Gln2 by Arg or of Ala44 by Lys is suggested to be responsible for the trypsin-inhibitory action of BGIT. Inhibitory activity of BGIT for trypsin was greatly decreased by acetylation, while that for subtilisin was slightly increased. From these results and the sequence comparison with eglin-c superfamily inhibitors, the reactive site of BGIT is assumed to be Lys44.