3.4.19.3 the heat denaturation of wild-type enzyme and mutant enzymes C188S and C142S/C188S is highly reversible in the dimeric forms, but completely irreversible in the tetrameric form 3.4.19.3 the heat-denaturation of the mutant enzyme C142S/C188S is completely reversible at pH 2.3, although the unfolding-refolding reactions are characterized by extremely slow kinetics