title: Partially folded conformations of inositol monophosphatase endowed with catalytic activity.
abstract: 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 microM. 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.
authors.affiliation: Department of Applied Biology and Chemical Technology, Hong Kong Polytechnic University, Hong Kong.
authors.forename: C K
authors.initials: CK
authors.lastname: Lau
authors.forename: S C
authors.initials: SC
authors.lastname: Lo
authors.forename: W
authors.initials: W
authors.lastname: Li
authors.forename: D R
authors.initials: DR
authors.lastname: Churchich
authors.forename: F
authors.initials: F
authors.lastname: Kwok
authors.forename: J E
authors.initials: JE
authors.lastname: Churchich
mesh_terms: D000818:Animals; D002384:Catalysis; D002850:Chromatography, Gel; D002942:Circular Dichroism; D003035:Cobalt / Q000378:metabolism; D019281:Dimerization; D004795:Enzyme Stability; D008274:Magnesium / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D013552:Swine; D014508:Urea / Q000737:chemistry