Energy transfer kinetics in C-phycocyanin from cyanobacterium Westiellopsis prolifica studied by pump-probe techniques.

The relaxation processes of C-phycocyanin at different aggregates have been investigated by pump-probe techniques. The lifetimes of ground state recovery measured at various wavelengths are analyzed by computer fitting of the kinetic data to a sum of three and four exponentials for monomers and trimers according to the nonlinear least-square principle, respectively. The shortest lifetime (about 56ps) is due to beta s----beta f transfer in one monomer, that decreases to 31ps in trimer due to the opening of new transfer channels. The second fastest component (about 151ps) in monomer is attributed tentatively to distribution of excitation energy between alpha and beta f chromophores, that decreases to about 117ps in trimer caused by redistribution of excitation energy between them. The two long-lived components (about 690ps and 1385ps for monomer, 620ps and 1320ps for trimer) from some kinds of heterogeneity in some chromophores, such as alpha and beta 1 chromophores which are emitting, show an equal amplitude ratio of 1:2 in both monomer and trimer.