Structural and functional determinants of Mucor miehei protease. V. Enthalpy changes upon thermal denaturation in solution of varying pH

Structural and functional determinants of Mucor miehei protease VI. Inactivation of the enzyme by diazoacetyl norleucine methyl esters, pepstatin and 1,2-epoxy-30(p-nitro-phenyoxy)propane

Mucor miehei protease (EC 3.4.21 -- ), an acid protease of fungal origin, was rapidly inhibited at pH 5.0 and 10 degrees C by a 78-fold molar excess of diazoacetyl norleucine methyl ester (N2Ac-Nle-OMe) when simultaneously added with a 78-fold molar excess of Cu(II). Preincubation with Cu(II) before the addition of N2Ac-Nle-OMe reduced the initial rate of activity loss presumably due to a copper-induced structural change as deduced from an examination of CD spectra. Cof norleucine and 1.02 +/- 0.041 mol of copper. The conformation of the N2Ac-Nle-OMe-inhibited enzyme appeared to be somewhat altered since the rate of H-3H exchange determined for the slowest exchanging class of hydrogens was reduced by more than 10-fold although the estimated number of hydrogens in this class remained constant. Mucor miehei protease was also inhibited by pepstatin; complete inactivation required a 6-fold molar excess of inhibitor and was associated with a major conformational change as determined from CD spectra. Loss of activity also occurred in the presence of 1,2-epoxy-3-(p-nitrophenyoxy)propane (EPNP).