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Effect of Na+ ions on pH-dependent conformational changes in brush border sucrase-isomaltase in mice intestine

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Title Effect of Na+ ions on pH-dependent conformational changes in brush border sucrase-isomaltase in mice intestine
 
Creator Gupta, Shiffalli
Mahmood, Safrun
Khan, Rizwan Hasan
Mahmood, Akhtar
 
Subject Brush border sucrase
Mice intestine
Alkali metal ions
pH-dependent effects
UV-CD spectral analysis
Fluorescence spectral studies
 
Description 399-403
Intestinal brush border sucrase-isomaltase (sucrose D-glucosidase E.C. 3.2.1.48, E.C. 3.2.1.10) exhibits pH-dependent stimulatory or inhibitory effects in response to Na⁺ ions. However, whether the enzyme undergoes conformational modulations as a function of pH and in the presence of alkali metal ions is not known. In this paper, we investigated the structural and functional relationship of purified murine sucrase in response to pH and Na⁺ ions using UV-CD fluorescence and spectroscopic studies. Kinetic studies revealed that at pH 5.0, the enzyme activation by Na⁺ ions was V-type, which changed to K-type at pH 7.2, whereas at alkaline pH (8.5), Na⁺ ions inhibited the enzyme activity and inhibition was uncompetitive in nature, affecting both the Km and Vmax components. Far UV-CD spectra of protein at pH 7.2 in the absence and presence of Na⁺ were almost overlapping, suggesting that secondary structure of protein was not affected upon addition of the salt. However, near UV-CD spectra indicated marked alterations in the tertiary structure of protein in presence of
50 mM Na⁺ ions. Increase in pH from 7.2 to 8.5 resulted in a marked rise in fluorescence intensity and red shift in λmax due to tryptophan residues in the enzyme molecule. These findings suggested that alterations in enzyme activity as a function of pH and Na⁺ ions was associated with ionization of key amino acid residues together with structural modifications in the enzyme conformation around neutral or alkaline pH.
 
Date 2008-12-31T06:08:33Z
2008-12-31T06:08:33Z
2008-12
 
Type Article
 
Identifier 0301-1208
http://hdl.handle.net/123456789/2707
 
Language en_US
 
Publisher CSIR
 
Source IJBB Vol.45(6) [December 2008]