title: Kinetics of binding of methyl alpha- and beta-D-galactopyranoside to peanut agglutinin: a carbon-13 nuclear magnetic resonance study.
abstract: The binding kinetics of methyl alpha- and methyl beta-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 10(4) M-1 s-1 for the alpha-galactopyranoside and 3.6 X 10(4) M-1 s-1 for the beta-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 degrees C for the alpha-galactopyranoside, and in the range of 9-39 s-1 within a temperature range of 5-25 degrees C for the beta-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.
mesh_terms: D002942:Circular Dichroism; D007700:Kinetics; D037102:Lectins; D009682:Magnetic Resonance Spectroscopy; D008756:Methylgalactosides; D008759:Methylglycosides; D019887:Peanut Agglutinin; D011485:Protein Binding; D011487:Protein Conformation; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D037102:Lectins; D008756:Methylgalactosides; D008759:Methylglycosides; D019887:Peanut Agglutinin