EQUILIBRIUM UNFOLDING STUDIES OF HORSE MUSCLE ACYLPHOSPHATASE

The stability and equilibrium unfolding behaviour of horse muscle acyl phosphatase have been studied by denaturing the protein under various conditions of temperature, pH, and urea concentration. Far-ultraviolet circular dichroism (CD) and nuclear magnetic resonance (NMR) spectros copy indicate that this small monomeric protein unfolds reversibly and cooperatively. Thermodynamic parameters, the Gibbs free energy Delta G and enthalpy Delta H of unfolding, have been estimated for denaturat ion of the protein from NMR and CD data as 19 kJ mol(-1) and 350 kJ mo l(-1), respectively. CD and H-1-NMR results suggest the presence of ve ry little persistent residual structure in the denatured states studie d under these different conditions. Furthermore, photo-chemically indu ced dynamic nuclear polarisation experiments show that in the denature d states aromatic residues are freely accessible to a flavin dye probe .