Solution Properties of Phycocyanin. IV. Studies of the Self-association Equilibrium of Phycocyanin in a pH 6.8 Solution

Publisher Website
Google Scholar
Abstract
The self-association of phycocyanin in a buffer of pH 6.8 with an ionic strength of 0.1 has been studied by sedimentation equilibrium measurements in the temperature range from 5.2 to 25 °C. The self-association of this system increases with a decrease in the temperature. A quantitative evaluation of the experimental data for this system indicates that the type of the association reaction is not a simple mechanism such as a monomer\ightleftharpoonsn-mer, but the discrete monomer\ightleftharpoonstrimer\ightleftharpoonstetramer mechanism is probable. Several thermodynamic quantities, such as the Gibbs free energy change, ΔG°, the enthalpy change, ΔH°, and the entropy change, ΔS°, accompanying the self-association reaction were computed on the basis of the equilibrium constants. From the results, it is considered that the association process is similar to the ordinary crystallization, and that the formation of a tetramer proceeds at a higher concentration than that in which the trimerization reaction is completed.