Allosteric serine hydroxymethyltransferase from monkey liver: Correlation of conformational changes caused by denaturants with the alterations in catalytic activity |
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Authors: | Kashi S Ramesh V S Anantanarayanan N Appaji Rao |
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Institution: | (1) Department of Biochemistry, Indian Institute of Science, 560 012 Bangalore;(2) Department of Biochemistry, Memorial University of Newfoundland, AIB 3x9 St. John’s, Newfoundland, Canada;(3) Present address: Hematology Research Laboratory, Massachusetts General Hospital, Harvard Medical School, 02114 Boston, Massachusetts, USA |
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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. |
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Keywords: | Serine hydroxymethyltransferase conformational changes denaturants fluorescence circular dichroism structure-activity relationship |
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