KINETICS OF INTERACTION BETWEEN RABBIT TRANSFERRIN AND RETICULOCYTES

Kinetic characteristics of the interaction between transferrin and reticulocytes have been studied using purified iron-saturated rabbit transferrin and rabbit reticulocytes. The effects of varying transferrin concentration, reticulocyte concentration, and temperature on rate constants for the association and dissociation reactions were measured. The activation energies required for the association and dissociation reactions (10.8 and 12.0 kcal mole-1, respectively) were not significantly different. The number of specific reticulocyte binding sites for transferrin was estimated to be about 300,000 sites/reticulocyte. The average equilibrium constant was 200,000 1. mole-1 and the average standard free-energy change for the reaction was -7.3 kcal mole-1. The standard enthalpy change was negligibly small, but there was a considerable increase in entropy for the reaction. These results may be interpreted as suggesting that the reticulocyte has available a limited number of binding sites specific for transferrin and bind transferrin by several weak bonds. © 1969, American Chemical Society. All rights reserved.