Protein aggregation in C-phycocyanin. Studies at very low concentrations with the photoelectric scanner of the ultracentrifuge

摘要

pSolutions of C-phycocyanin of very low concentrations were examined by sedimentation-velocity studies in the Spinco model E ultracentrifuge equipped with a photoelectric scanning system and a monochromator. At sufficiently low concentrations complete disaggregation from the hexamer to the monomer was observed. The equilibrium constant of monomer to hexamer was estimated to be approx. 10sup30/sup. For studies of aggregation over the complete range of concentration, C-phycocyanins from iPhormidium luridum/i and iLyngbya/i sp. were used. Sedimentation-velocity studies at high concentration with schlieren optics are reported for C-phycocyanins from iAnabaena variabilis/i and iLyngbya/i sp. The pH-dependence of aggregation and the temperature-dependence of trimer–hexamer equilibrium for phycocyanins from these algae were found to be similar to those of other C-phycocyanins. The principal feature of the pH-dependence is the dominance of hexamers at the isoelectric point. Increasing temperature increased the amount of hexamer and decreased the amount of trimer./p