MUNG BEAN TRYPSIN-INHIBITOR - SYNTHESIS OF A FRAGMENT AND ITS ANALOGS

The Lys active fragment of the mung bean trypsin inhibitor is composed of two peptide chains, one with 26 amino acid residues and the other with 9 residues linked by two interdisulfide bonds. The two peptide ch ains could be separated successfully from each other by reduction with DTT followed by gel filtration. The reduced long peptide chain contai ning 6 Cys residues was subjected to air oxidation, and about 25% of t he original antitrypsin activity of the Lys fragment was recovered. Fo llowing the previously reported sequence, the solid-phase synthesis of this long peptide chain and its disulfide bond refolding are presente d. Unexpectedly, the synthetic peptide showed much lower antitrypsin a ctivity than the natural one after reduction and air reoxidation. In o rder to explain this uncompatible result, we redetermined the sequence of the native long peptide chain of the Lys active fragment and obtai ned the result that the P'(2) position is Ile instead of Lys as previo usly reported. To ascertain the correct sequencer we synthesized anoth er 22-peptide following the newly determined 26-peptide sequence, and skimming two residues respectively from N-terminus and C-terminus. Aft er reduction and reoxidation, the synthetic 22-peptide had the same an titrypsin activity as that of the native 26-peptide. Meanwhile, an ana logue of this 22-peptide in which the residue Lys at the reactive site was replaced by Ala was also synthesized. This synthetic analogue did not show any activity either to trypsin or to elastase.