Chromophore interactions in allophycocyanin

Abstract

Allophycocyanin [of blue-green and red algae], which is normally isolated as a trimer (.alpha.3.beta.3), was successfully dissociated into a monomer (.alpha..beta.) with different spectroscopic properties. Upon dissociation the characteristic 650 nm absorption and 661 nm fluorescence emission bands of the trimer are completely lost and its fluorescence polarization properties are sharply altered. Spectroscopic characteristics of allophycocyanin monomers are much closer to those of C-phycocyanin than to trimeric allophycocyanin. A model for trimeric allophycocyanin is presented in which the appearance of the 650 nm absorption band is induced by a particular kind of chromophore-chromophore interaction. Similar results are found for both allophycocyanin II and III.