Spectral and conformational characteristics of phycocyanine associated with changes of medium pH

Abstract

Abstract C-phycocyanin (C-PC) is the main component of water-soluble light-harvesting complexes of cyanobacteria. These complexes are involved in the absorption of quantum energy and the transfer of electron excitation energy to photosystems. A specific environment of C-PC chromophoric groups is provided by the protein matrix structure including protein-protein contacts between different subunits. Registration of C-PC spectral characteristics and the kinetics of a fluorescence anisotropy damping have revealed a significant pH influence on the chromophore microenvironment: at pH 5.0, a chromophore is more significantly interacts with a solvent, whereas at pH 9.0 the chromophore microenvironment becomes more viscous. Conformations of a chromophore and a C-PC protein matrix have been studied by Raman and infrared spectroscopy. A decrease in the medium pH results in changes in the secondary structure of both C-PC and chromophore making the last one to be more convoluted.