| Résumé | The binding kinetics of methyl α- and methyl β-D-galactopyranoside to the anti-T lectin from peanuts were studied by ¹³C NMR, employing methyl galactopyranosides specifically enriched in ¹³C at C-1. Association and dissociation rate constants, as well as their activation parameters, are reported. The association rate constants, 4.6 X l0⁴ M⁻¹ s⁻¹ for the α-galactopyranoside and 3.6 X l0⁴ M⁻¹ s⁻¹ for the β-galactopyranoside, are several orders of magnitude below those expected for a diffusion-controlled process. For both anomers, the association rate constant was temperature independent, implying that the association process occurs without a significant activation enthalpy. However, a considerable association activation entropy was found for both ligands. The dissociation rate constants were in the range of 9-46 s⁻¹ within a temperature range of 5-35 ºC for the a-galactopyranoside, and in the range of 9-39 s⁻¹ within a temperature range of 5-25 ºC for the β-galactopyranoside. A considerable dissociation activation enthalpy of ca. 10 kcal mol⁻¹ was found for both anomers. A two-step binding model, consistent with the present NMR data and with previous UV and CD spectroscopic data, is presented. |
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