KINETICS AND MECHANISM FOR THE CONFORMATIONAL TRANSITION IN p-GUANIDINOBENZOATE BOVINE TRYI’SINOGEN INDUCED BY THE ISOLEUCINE-VALINE DIPEI’TIDE H.J. NOLTE and E. NEUMANN

The interaction between p-guanidmobenzoate-trypsinogen and the isoleucine-valine dipeptide has been investigated by temperature-jump relaxation spectrometry. Using the absorbance at 281 nm the concentration dependence of the relaxation parameters is consistent with the conventional induced-fit model: rapid ligand bindin, u coupled to a slower intramolecular change; some alternative mechanisms can be excluded. At 296 R, 0.1 M Tris HCI, pH = 7.4, the dissociation equilibrium constant for the overall process isK = zS.l(iO.2) X 16’ hl; for the binding step Kt = 2_3(%0.3) X lob3 hl and the rate constants for the structural change are k2 = 26(~6)s-’ and k, = 0.6 l(? 0.04)s-’ ; the overall dissociation reaction enthalpy is aHo = 26(*6) kJmoT’ and the reaction entropy is AS0 = 4(+20) kJiT-’ mol-‘. In combination with CD and X-ray crystallographic data, the results of this study suggest that the binding of the dipeptide to a trypsinogen-like, partially disordered conformation induces a transition to a trypsin-like highly ordered structure.