Association and dissociation of phycocyanin by small molecules

Sedimentation velocity experiments showed that tetraalkylammonium salts, with alkyl chain lengths ranging from methyl to pentyl and in the concentration range from 0.02 to 0.16 m, decrease the aggregation of C-phycocyanin in sodium phosphate buffers, pH 6.0 and 7.0, I 0.1, at 23 °C.Tetrabutylammonium and tetrapentylammonium bromides and chlorides disaggregate 11S and 17S C-phycocyanin aggregates to produce a 6S subunit. The larger alkyl group produces the greater effect. An explanation for this effect would be that hydrophobic and possibly ionic interactions between the protein and the tetraalkylammonium cation effectively block assembly of the 6S to 11S aggregate. These salts may provide a novel means for the control of protein assembly.Recent studies on the effect of neutral aromatic compounds on C-phycocyanin aggregation were extended to saturated solutions of α- and β-naphthol, with concentrations of <0.003 and <0.006 m, respectively. Sedimentation velocity experiments and absorption spectroscopy suggest that the aggregation of C-phycocyanin is increased by naphthol binding to the protein.