Solution Properties of Phycocyanin. V. Studies of the Self-association Reaction of Phycocyanin in a pH 5.4 Solution

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Abstract
The self-association of phycocyanin in a buffer solution of pH 5.4 with an ionic strength of 0.1 has been studied by sedimentation equilibrium measurements in the temperature range from 5.0 to 25.0 °C. The thermodynamical treatment is also presented. The self-association of phycocyanin molecules proceeds with a decrease in the temperature. The concentration dependence of the apparent weight-average molecular weight of phycocyanin is interpreted in terms of a monomer\ightleftharpoonshexamer equilibrium system. It is clear from the thermodynamic parameters, ΔG0, ΔH0, and ΔS0, that the self-association reaction is spontaneous in the solution of pH 5.4. In the association process, the formation of hydrophobic bonds is suggested by the large positive entropy change accompanying association reaction of phycocyanin molecules.