Purification, crystallization and preliminary crystallographic investigations of selenium-containing phycocyanin from selenium-rich algae (Spirulina platensis)

The selenium-containing phycocyanin from the selenium-rich algae (Spirulina platensis) has been crystallized in two crystal forms by the hanging-drop vapor diffusion techniques. A chromatographic procedure of gel filtration a nd anion exchange was used for purification. Form I crystal with space grou p P2(1) and cell parameters a = 108.0 Angstrom, b = 117.0 Angstrom, c = 184 .0 Angstrom, beta = 90.2 degrees and 12(alpha beta) units in the asymmetric unit was obtained by using (NH4)(2)SO4 as precipitant. These crystals diff ract up to 28 Angstrom. Form II crystal obtained by using PEG4000 as precip itant belongs to space group P6(3) with unit cell constants a = 155.0 Angst rom, c = 40.3 Angstrom, gamma = 120.0 degrees and one(alpha beta) unit in t he asymmetric unit. The crystals diffract beyond 2.9 Angstrom. The possible stacking forms of phycocyanin molecules in the first crystal form were dis cussed.