Partially folded conformations of inositol monophosphatase endowed with catalytic activity

C. K. Lau, Chun Lap Samuel Lo, W. Li, D. R. Churchich, F. Kwok, J. E. Churchich

Research output: Journal article publicationJournal articleAcademic researchpeer-review


The stability of porcine brain inositol monophosphatase in the presence of increasing concentrations of urea was investigated at pH 7.5. Exposure of the enzyme to 8 M urea brings about the dissociation of the dimeric species of 58 kDa into monomeric forms as revealed by gel filtration chromatography. Unfolding of the protein by 8 M urea results in a decrease of the ellipticity at 220 nm (20%) together with a perturbation of the near-UV circular dichroism spectrum. Urea-treated inositol monophosphatase binds Co2+ ions with a dissociation constant of 3.3 μM. The enzyme is catalytically competent when assayed with 4-nitrophenyl-phosphate in the presence of the activating ion Co2+ at pH 7.5 in 8 M urea. The apparent activation constant for Co2+ is 2.5 mM. It is postulated that partially folded conformations of monomeric species preserve their catalytic function because the affinity of Co2+ ions for the metal coordination center of the protein is not perturbed by exposure to 8 M urea.
Original languageEnglish
Pages (from-to)789-797
Number of pages9
JournalJournal of Protein Chemistry
Issue number8
Publication statusPublished - 1 Dec 1998


  • Folding
  • Inositol monophosphatase
  • Molten globule
  • Monomeric species
  • Urea denaturation

ASJC Scopus subject areas

  • Biochemistry


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