Thermodynamic and kinetic studies on saccharide binding to soya-bean agglutinin.

Swamy, MJ and Sastry, M V Krishna and Khan, MI and Surolia, A (1986) Thermodynamic and kinetic studies on saccharide binding to soya-bean agglutinin. In: Biochemical Journal, 234 (3). 515 -522.

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Abstract

The fluorescence of N-dansylgalactosamine [N-(5-dimethylaminonaphthalene-1-sulphonyl)galactosamine] was enhanced 11-fold with a 25 nm blue-shift in the emission maximum upon binding to soya-bean agglutinin (SBA). This change was used to determine the association constants and thermodynamic parameters for this interaction. The association constant of 1.51 X 10(6) M-1 at 20 degrees C indicated a very strong binding, which is mainly due to a relatively small entropy value, as revealed by the thermodynamic parameters: delta G = -34.7 kJ X mol-1, delta H = -37.9 kJ X mol-1 and delta S = -10.9 J X mol-1 X K-1. The specific binding of this sugar to SBA shows that the lectin can accommodate a large hydrophobic substituent on the C-2 of galactose. Binding of non-fluorescent ligands, studied by monitoring the fluorescence changes when they are added to a mixture of SBA and N-dansylgalactosamine, indicates that a hydrophobic substituent at the anomeric position increases the affinity of the interaction. The C-6 hydroxy group also stabilizes the binding considerably. Kinetics of binding of N-dansylgalactosamine to SBA studied by stopped-flow spectrofluorimetry are consistent with a single-step mechanism and yielded k+1 = 2.4 X 10(5) M-1 X s-1 and k-1 = 0.2 s-1 at 20 degrees C. The activation parameters indicate an enthalpicly controlled association process.

Item Type:	Journal Article
Publication:	Biochemical Journal
Publisher:	Portland Press
Additional Information:	Copyright of this article belongs to Portland Press.
Department/Centre:	Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited:	09 Feb 2010 09:21
Last Modified:	19 Sep 2010 05:41
URI:	http://eprints.iisc.ac.in/id/eprint/22406

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