Kinetic and equilibrium aspects of human albumin adsorption onto biological apatite beads

Abstract

Albumin adsorption onto human enamel beads (HEB) was studied at equilibrium and kinetically with an experimental set-up allowing continuous monitoring with time of the excess interfacial protein concentration. Assuming a Langmuir adsorption model and applying the mass conservation law, it was possible to calculate the adsorption and desorption rate constants k a and k d and thus the affinity constant K which is compared with the corresponding value deduced from equilibrium studies. Three ( k a, k d) pairs were generally necessary to fit the kinetic data over the whole adsorption domain. The initial “fast” regime was attributed to a Na + coadsorption process, followed by two “slower” regimes in which adsorption rates increased with the interfacial residence time of the protein. A cooperative effect of the already adsorbed, and probably partly denatured, molecules was proposed to explain these unexpected results.