Thermodynamics of the binding of chymotrypsin with the black-eyed pea trypsin and chymotrypsin inhibitor (BTCI)

The binding of alpha-chymotrypsin to black-eyed pea trypsin/chymotrypsin in hibitor (BTCI) has been studied using the inhibitory activity against the e nzyme and the formation of the complex enzyme/ inhibitor followed by measur ements of fluorescence polarization. Apparent equilibrium constants were es timated for several temperatures and the values obtained range from 0.32 x 10(7) to 1.36 x 10(7) M-1. The following values were found from van't Hoff plots: Delta H(vh)degrees = 10.8 kcal mol(-1) (from inhibitory assays) and 11.1 kcal mol(-1) (from fluorescence polarization); Delta S degrees = 67.9 and = 67.8 kcal K-1 mol(-1) respectively. Calorimetric binding enthalpy was determined (corrected for the ionization heat of the buffer) and the resul ting value was Delta H(cal)degrees = 4.9 kcal mol(-1). These results indica te that the binding of chymotrypsin to BTCI is an entropically driven proce ss.