STUDIES ON THE DISSOCIATION OF CRYPTOMONAD BILIPROTEINS

The spectroscopic properties of two biliproteins, phycocyanin 645 and phycoerythrin 566, have been studied by treating the proteins with two different agents, NaSCN at pH 6.0, or pH 4.0 without NaSCN, For phyco erythrin 566, treatment with NaSCN revealed that the visible CD spectr um of its chromophores was separated into a pair of different spectra, and each of these spectra was observed as a negative and one or more positive bands, For phycocyanin 645, two negative CD bands have been o bserved previously, together with two or more positive bands, in the d imer (alpha(2) beta(2)) state, and NaSCN treatment caused elimination of one of these negative bands. The dimer was stable at pH 6.0, but at pH 4.0 the spectra of phycocyanin 645 had one less negative band than those at pH 6.0. Chromatography demonstrated that phycocyanin 645 was a monomer (alpha beta) at pH 4.0. Monomers of cryptomonad biliprotein s have never been observed before, Excitation at 514 nm, in picosecond time resolved fluorescence studies, produced lifetimes of 11.0 and 45 .2 ps for dimers and monomers, respectively, Excitation at 566 nm yiel ded times of 1.38 and 1.24 ps, for dimers and monomers, respectively. CD in the far UV showed that monomers and dimers had very similar seco ndary structures. These results have been used to test an hypothesis t hat proposed two types of exciton splitting among the chromophores of phycocyanin 645, and perhaps phycoerythrin 566 could also have this ch romophore organization.