We studied bovine serum albumin (BSA) and alpha-chymotrypsin adsorption onto mica
surfaces over a large pH range by atomic force microscopy (AFM) measurements in liquid.
Data analyses (height, roughness and roughness factor) brought new insights on the
conformation of proteins in soil environments, with mica as a model of soil phyllosilicates
and non-hydrophobic surfaces. Validation of AFM approach was performed on BSA, whose
behavior was previously described by nuclear magnetic resonance and infra-red spectroscopic
methods. Maximum adsorption was observed near the isoelectric point (IEP). A stronger
interaction and a lower amount of adsorbed proteins were observed below the IEP, which
contrasted with the progressive decrease of adsorption above the IEP. We then studied
the adsorption of alpha-chymotrypsin, a proteolytic enzyme commonly found in soils.
AFM pictures demonstrated a complete coverage of the mica surface at the IEP in contrast
to the BSA case. Comparison of the AFM data with other indirect methods broadened
the understanding of alpha-chymotrypsin adsorption process through the direct display
of the protein adsorption patterns as a function of pH.