FTIR-ATR AND RADIOLABELING STUDY OF THE ADSORPTION OF RIBONUCLEASE-A ONTO HYDROPHILIC SURFACES - CORRELATION BETWEEN THE EXCHANGE-RATE AND THE INTERFACIAL DENATURATION

The kinetic aspects of the exchange mechanism and of the ongoing struc tural modification with interfacial residence time for ribonuclease A adsorbed on hydrophilic surfaces are investigated. This is done by mea ns of radiolabeling and FTIR-ATR techniques. An important decrease of the protein exchange ability and increase of the irreversibly bound pr otein fraction with adsorption time is found. These observations are c ompared with a decrease of the relative content of beta-sheet and an i ncrease in turns and unordered structures in the adsorbed protein laye r. Both the exchange process and the structural modifications vary wit h comparable characteristic times, on the order of 20 h for the exchan ge process on the TiO2 surface and 10-15 h for the structural modifica tions on the germanium one. These data suggest that the decrease in th e protein exchange ability results from important structural changes f ollowing adsorption, which corresponds to a decrease of the ordered st ructure of the protein.