Langmuir and scatchard parameters do not describe the binding of Actinomyces viscosus to saliva-treated hydroxyapatite.

The binding of Actinomyces viscosus T14V to saliva-treated spheroidal hydroxyapatite (SHA) beads was studied. The association constant (K) and the total number of binding sites (N) obtained from the Langmuir plots were in good agreement with those reported by other workers (approx. 3 X 10(-8) and 3 X 10(8), respectively). The values for N obtained from Scatchard plots differed from those obtained from Langmuir plots by factors of 10(6) or more. These results suggest that either these equations are inappropriate to describe binding or certain assumptions regarding this system are not being met. The use of these models requires, among other constraints, that the process be reversible and that measurements be taken at equilibrium. A method was developed which allowed a close examination of the equilibrium dynamics without perturbation of the system. The results suggest that the adsorption process is only poorly reversible. Adsorption to SHA was not at equilibrium after 1.5 h. Even when bacteria were allowed to adsorb for longer periods, and the system appeared to approach equilibrium, the increased time of adherence did not significantly alter the derived K or N values. Our results suggest that the use of Scatchard and Langmuir plots is inappropriate to describe binding of A. viscosus to SHA.