Adsorption of trypsin on hydrophilic and hydrophobic surfaces

The adsorption of trypsin onto polystyrene and silica surfaces was investigated by reflectometry, spectroscopic methods, and atomic force microscopy (AFM). The affinity of trypsin for the hydrophobic polystyrene surface was higher than that for the hydrophilic silica surface, but steady-state adsorbed amounts were about the same at both surfaces. The conformational characteristics of trypsin immobilized on silica and polystyrene nanospheres were analyzed in situ by circular dichroism and fluorescence spectroscopy. Upon adsorption the trypsin molecules underwent structural changes at the secondary and tertiary level, although the nature of the structural alterations was different for silica and polystyrene surfaces. AFM imaging of trypsin adsorbed on silica showed clustering of enzyme molecules. Rinsing the silica surface resulted in 20% desorption of the originally adsorbed enzyme molecules. Adsorption of trypsin on the surface of polystyrene was almost irreversible with respect to dilution. After adsorption on silica the enzymatic activity of trypsin was 10 times lower, and adsorbed on polystyrene the activity was completely suppressed. The trypsin molecules that were desorbed from the sorbent surfaces by dilution with buffer regained full enzymatic activity.