Trypsin and chymotrypsin inhibitor of Vigna unguiculata seeds--involvement of tyrosyls in its interaction with proteases.

When trypsin and chymotrypsin inhibitor of Vigna unguiculata seeds (black-eyed pea trypsin and chymotrypsin inhibitor, BTCI) combines with beta-trysin, 4.0, 4.5, 5.0, 5.8, and 6.6 tyrosyl residues are shielded from reaction with N-acetylimidazole, at reagent/protein molar ratios of 60, 120, 200, 350 and 500, respectively. This may result from the presence of tyrosyl residues in the zone of contact between enzyme and inhibitor. In the interaction of BTCI and alpha-chymotrypsin, only 0.6 tyrosyl residues are shielded from the reaction with N-acetylimidazole, at a 500-fold reagent molar excess.