Abstract

C-phycocyanin and allophycocyanin are light-harvesting proteins that occur in the phycobilisome in cyanobacteria.¹ They represent relatively simple systems in which the structural factors that govern the direction and rate of excitation transfer can be addressed through the methods of picosec-ond spectroscopy. Several aspects of the structure of C-phycocyanin, as recently determined by X-ray crystallographic methods,² present challenges to current theories for excitation transfer in light-harvesting proteins. We have begun a detailed characterization of the picosecond transient absorption and dichroism kinetics of C-phycocyanin in order to compare measured patterns of excitation transfer in C-phycocyanin with those indicated by direct calculation, using the known coordinates and orientations of the pigment molecules bound by the protein. We are also examining excitation transfer processes in allophycocyanin, a similar phycobiliprotein that directs excitation energy received from C-phycocyanin towards the photosystem II reaction center.

© 1990 Optical Society of America