The state of the single tryptophyl of the black-eyed pea trypsin and chymotrypsin inhibitor by charge transfer with N-methylnicotinamide chloride.

The single tryptophan residue of the black-eyed pea trypsin and chymotrypsin inhibitor was found to be sufficiently exposed to bind N-methylnicotinamide chloride and give rise to a characteristic charge-transfer absorption spectrum. At pH 7.0, ionic strength of 1M and 25 degrees C, an apparent association constant K = 3.19 +/- 0.07 M-1 and a molar extinction coefficient epsilon = 1240 +/- 18 M-1 cm-1 (at 350 nm) were obtained for the charge-transfer complex. The values of these parameters were also estimated for other wavelengths over the 330-420 nm range. The association constant showed a negligible dependence on the wavelength.