• Allosteric serine hydroxymethyltransferase from monkey liver: Correlation of conformational changes caused by denaturants with the alterations in catalytic activity

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    • Keywords


      Serine hydroxymethyltransferase; conformational changes; denaturants; fluorescence; circular dichroism; structure-activity relationship

    • Abstract


      The far-ultraviolet region circular dichroic spectrumof serine hydroxymethyltransferase from monkey liver showed that the protein is in an α-helical conformation. The near ultraviolet circular dichoric spectrum revealed two negative bands originating from the tertiary conformational environment of the aromatic amino acid residues. Addition of urea or guanidinium chloride perturbed the characteristic fluorescence and far ultraviolet circular dichroic spectrum of the enzyme. The decrease in (θ)222 and enzyme activity followed identical patterns with increasing concentrations of urea, whereas with guanidinium chloride, the loss of enzyme activity preceded the loss of secondary structure. 2-Chloroethanol, trifluoroethanol and sodium dodecyl sulphate enhanced the mean residue ellipticity values. In addition, sodium dodecyl sulphate also caused a perturbation of the fluorescence emission spectrum of the enzyme. Extremes of pH decreased the — (θ)222 value. Plots of — (θ)222and enzyme activity as a function of pH showed maximal values at pH 7.4–7.5. These results suggested the prevalence of “conformational flexibility” in the structure of serine hydroxymethyltransferase.

    • Author Affiliations


      Kashi S Ramesh1 2 V S Anantanarayanan1 3 N Appaji Rao1

      1. Department of Biochemistry, Indian Institute of Science, Bangalore - 560 012
      2. Hematology Research Laboratory, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts - 02114, USA
      3. Department of Biochemistry, Memorial University of Newfoundland, St. John’s, Newfoundland - AIB 3x9, Canada
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