Conformational change of bovine serum albumin molecules at neutral pH in ultra-diluted aqueous solutions.

Surface chemical and electrochemical techniques were applied to reveal the unfolding of bovine serum albumin (BSA) molecules induced by concentrations in aqueous solution. Real-time surface pressures vs time (pi-t) kinetic curves were recorded over an aqueous subphase (190 mL) by spreading BSA solutions of different concentrations but of the same amount (8.0 x 10(-4) mg) at the air/water (A/W) interface. A critical concentration (similar to 1.0 ppm) was discovered below which the surface pressure declines with time and the BSA is totally solubilized in the water subphase. Above this critical concentration (e.g., 8.0 ppm), the surface pressure goes up and the protein molecules assemble into a Langmuir monolayer at the A/W interface. These findings demonstrate that the BSA molecules have different conformations in the spreading protein solutions. The conformational transition in BSA molecules induced by concentrations was also confirmed by spectroscopy means and the catalytic hydrogen evolution reaction on a silver amalgam electrode by using constant current chronopotentiometric stripping. This discovery fills in gaps of Foster's N (normal) -> F (fast) model, in which the unfolding of BSA molecules occurs at neutral pH values (8.0-4.3).