[Interaction between ricin hemagglutinin and its ligands, galactose and lactose. Microcalorimetry and equilibrium dialysis].
The interaction of Ricinus communis hemagglutinin with galactose and lactose has been studied by means of microcalorimetry, equilibrium dialysis and analytical ultracentrifugation. A first class of beta-galactoside-binding sites involves two similar and independent sites of which affinity constants are 2600 M-1 for galactose and 26700 M-1 for lactose at 25 degrees C. The binding of one galactose or one lactose molecule leads to enthalpy changes of--12.3 Kcal and--11 Kcal, respectively. Considering the negative entropy changes of the association, and as for ricin, the binding of galactosides with hemagglutinin is driven by favorable enthalpic contributions. In presence of high lactose concentrations, a second endothermic step of the calorimetric titration curve was observed. This result and the biphasic nature of Scatchard plots of equilibrium dialysis suggest the existence of a second class of binding sites on the lectin molecule. As  for ricin, the interaction between these secondary sites and lactose would be entropically driven.
D000373:Agglutinins; D001665:Binding Sites; D002151:Calorimetry; D003956:Dialysis; D005690:Galactose; D006388:Hemagglutinins; D007700:Kinetics; D007785:Lactose; D008024:Ligands; D012276:Ricin; D013816:Thermodynamics
D000373:Agglutinins; D006388:Hemagglutinins; D008024:Ligands; D012276:Ricin; D007785:Lactose; D005690:Galactose
Interaction entre l'hémagglutinine de ricin et ses ligands, galactose et lactose. Etude par microcalorimétrie et dialyse à l'équilibre.