Structure-function analysis of the emulsifying and interfacial properties of apomyoglobin and derived peptides

Apomyoglobin was chosen as a model to study the emulsifying properties of p roteins. It was cleaved into three peptides using cyanogen bromide and thes e peptides were purified and tested for emulsifying and interfacial propert ies. Two of the peptides had improved emulsifying activity compared to the whole protein. The peptide (residues 1-55) with the highest emulsifying act ivity and whole apomyoglobin were studied further. The amount of protein or peptide adsorbed at the oil-water interface of an emulsion was measured an d the surface area occupied per molecule was calculated. For apomyoglobin, at maximal surface coverage each molecule occupied a surface area of simila r to 8 nm(2). This is consistent with a packed monolayer, based on the appr oximate dimensions of apomyoglobin. For peptide (1-55), at maximal surface coverage each molecule occupied a surface area of similar to 3 nm(2). This is consistent with the area that the two amphipathic alpha-helices which ar e potentially present in this molecule would cover, if they were aligned al ong the oil-water interface. The different structural characteristics of th ese molecules responsible for their emulsifying properties are discussed. ( C) 1999 Academic Press.