ABSTRACT
UDP-galactose 4-epimerase from Escherichia coli is a homodimer of 39 kDa subunit with non-covalently bound NAD acting as cofactor. The enzyme can be reversibly reactivated after denaturation and dissociation using 8 M urea at pH 7.0. There is a strong affinity between the cofactor and the refolded molecule as no extraneous NAD is required for its reactivation. Results from equilibrium denaturation using parameters like catalytic activity, circular-dichroism, fluorescence emission (both intrinsic and with extraneous fluorophore 1-aniline 8-naphthalene sulphonic acid), 'reductive inhibition' (associated with orientation of NAD on the native enzyme surface), elution profile from size-exclusion HPLC and light scattering have been compiled here. These show that inactivation, integrity of secondary, tertiary and quaternary structures have different transition mid-points suggestive of non-cooperative transition. The unfolding process may be broadly resolved into three parts: an active dimeric holoenzyme with 50% of its original secondary structure at 2.5 M urea; an active monomeric holoenzyme at 3 M urea with only 40% of secondary structure and finally further denaturation by 6 M urea leads to an inactive equilibrium unfolded state with only 20% of residual secondary structure. Thermodynamical parameters associated with some transitions have been quantitated. The results have been discussed with the X-ray crystallographic structure of the enzyme.
Subject(s)
Binding Sites , Chromatography, High Pressure Liquid , Circular Dichroism , Dimerization , Enzyme Reactivators/pharmacology , Escherichia coli/enzymology , Kinetics , NAD/metabolism , Protein Conformation , Protein Denaturation , Protein Folding , Thermodynamics , UDPglucose 4-Epimerase/antagonists & inhibitorsABSTRACT
The Kinetic properties of plasma placental alkaline phosphatase patients with Chagas' disease were studied. When Cl2 Mg was used as activator the same increase of activity (17-20 per cent) was found in the chagasic and non chagasic groups. The enzyme was not inhibited by F-ion in any of the groups. No significant differences were detected between the two groups (chagasic and non chagasic) when the enzyme was treated with inhibitors such as EDTA and L-phenylamine. However, when the CN- ion was used, the enzyme of the normal pregnant women followed a Michaelian curve, whereas in the chagasic group a sigmoideal plot was observed. Thus, the Hill coefficient was 1.1 for the normal group and over 1.5 for the chagasic.