Reversible unfolding of myo-inositol monophosphatase

myo-Inositol monophosphatase isolated from pig brain is a very stable dimeric protein characterized by a rotational correlation time of 30 ns. The unfolding and dissociation of the dimeric enzyme (58 kDa) by guanidine hydrochloride have been investigated at equilibrium. The overall process was reversible as judged from the complete recovery of catalytic activity after dilution of guanidine hydrochloride-treated samples. Unfolding of myo-inositol monophosphatase was monitored by circular dichroism, fluorescence, and steady state emission anisotropy. A folded, monomeric form of the monophosphatase was not detected by the method of denaturant gel filtration. Uncoupled dissociation and unfolding of the oligomeric enzyme could not be demonstrated. The circular dichroism and emission anisotropy results are consistent with a model in which the dimeric protein unfolds in a single cooperative transition from folded dimer to two unfolded monomers.