Solution properties of a cell wall protein fromAcetabularia (Polyphysa) cliftonii

Studies have been performed on the precipitation of a cell wall protein, isolated from the marine green algaAcetabularia, from dilute aqueous solutions over the pH range where the α-helical conformation is maintained. The major purpose of this study was to establish the molecular conformation of a naturally occurring polypeptide of a molecular weight of 14,000 in the precipitate and to outline the mechanism of the precipitation. Since the precipitation behaviour from homogeneous protein solutions is important in relation to solution properties of the cognate polysaccharide chain from this alga, it was necessary to investigate the different conformations of the cell wall protein, including the possible aggregational states. Utilizing molecular weight fractions it can be shown that there are two distinctly different precipitation regions that depend on temperature, concentration of the protein, and pH. In one of these regions, the so-called α-region, precipitation occurs only in the α-helical conformation, without any conformational change if the physical conditions are varied. The temperature coefficient of the precipitation process in this α-region indicates that it must be nucleation controlled.