Surface properties of phycocyanin

The change of surface pressure (π) during adsorption and compression of phycocyanin film at the air-water interface indicates that this phycobiliprotein is strongly attracted to the interface. It behaves like a flexible molecule but is not completely unfolded. The steep slope of the curve of π as a function of the bulk concentration ( C b), when ( C b < 10 −3 mg/ml, may be attributed to the high number of hydrophobic amino acid residues and other structural features of the protein. At ( C b > 10 -3 mg/ml the π vs ( C b curve is interpreted as being characteristic of aggregation of the protein. Analysis of the curves of π vs ( C b and π vs molecular area ( A) indicate that the phycocyanin's tetrapyrrole chromophores make only a small contribution to the surface properties of the protein.