The determination of work of compression of protein monolayers at the air-water interface

Summary In the present study, monolayers of various proteins were investigated at the air-water interface. The work of compression,W _c (Helmholtz free energy) has been determined from the surface pressure-area compression isotherms. A linear relationship was found betweenW _c and the amount of protein present at the surface. Further, it is shown that this relation holds both for completely unfolded (Bovine-serum-albumin, Ovalbumin) and for incompletely unfolded (Transferrin, Myoglobin) proteins.β-Lipoprotein isotherms also gave a similar dependence. It is further shown that the amount of protein lost into the subphase can be determined from a plot ofW _c versus protein added at the interface. The results are discussed in relation to the constitution of protein molecules at the surface.