PROTEIN ADSORPTION FROM SEAWATER ONTO SOLID SUBSTRATA .1. INFLUENCES OF SUBSTRATUM SURFACE-PROPERTIES AND PROTEIN-CONCENTRATION

To model non-specific protein adsorption in seawater, partitioning of the plant enzyme, ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO), from seawater onto a variety of materials (Ti, Cu, Fe, PTFE [Teflon], Polycarbonate, Pyrex) was examined as functions of time and bulk concentration. Protein film thicknesses on titanium and copper varied temporally over 24 h in a laminar flow regime, increasing rapidly in the first hour on both metals and continuing to increase slowly on Ti but decreasing on Cu in the subsequent 15-23 h. Films also varied spatially from 0 to 28 nm on Ti and from 20 to 160 nm on Cu. Desorption kinetics of protein monolayers bound to Ti oxide surfaces were twice as rapid as those bound to Cu oxides. Proteins in overlying layer(s) of multilayered films, bound only to other proteins, desorbed more rapidly than molecules bound to metal oxide surfaces, irrespective of the type of substratum. Isothermic adsorption studies of H-3-RuBisCO indicated that surface concentrations were best described as a first-order function (GAMMA = KC01/n) of bulk protein concentration, C0, which was varied from 0.001 to 1050 mug cm-3. Surface films varied in thickness from submono- to multilayer coverage. Each substratum material exhibited significantly different binding capacities (K) and adsorption intensities (1/n) and at moderate bulk protein concentrations (10 mug cm-3) yielded an overall ranking of adsorption equilibria as follows: Pyrex< PTFE < Ti < PC < Cu <Fe. While the chemical composition of the substratum surfaces varied widely among the six materials tested, the initial critical surface tensions (CST) of these surfaces accounted for 87% of the variance observed in adsorption intensity, 1/n, (excluding Pyrex). In seawater, bulk concentration and substratum CST were shown to be critical in determining rates of non-specific protein adsorption and desorption as well as partitioning equilibria. Results illustrate the complexity of protein adsorption in seawater indicative of multilayered, heterogeneous adsorption at the surface.