A comparison of cryptophytan phycocyanins

Abstract

The spectroscopically different phycocyanins present in the type strain of Hemiselmis virescens, Millport 64, and in a second strain of this cryptophytan species, Plymouth 157, have been purified and compared. They are similar in native molecular weight and in subunit structure, both containing α and β subunits with molecular weights of approximately 10 000 and 19 000 respectively. However, they do not have the same chromophore composition. Both subunits of the phycocyanin of Plymouth 157 contain two bilins, with absorption maxima at 600 and 660 nm, respectively. Only the β subunit of Millport 64 carries these chromophores; its α subunit bears another chromophore, with absorption maxima at 368 and 694 nm. The spectroscopic differences between the two native phycocyanins can be entirely accounted for by their differing chromophore compositions. The phycocyanin of Millport 64 is the only biliprotein so far described which contains three chemically different chromophores.