Purification, crystallization and preliminary crystallographic investigations of selenium-containing phycocyanin from...

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 and anion exchange was used for purification. Form I crystal with space group P2(1) and cell parameters a =108.0 A, b= 117.0 A, c = 184.0 A, beta= 90.2 degrees and 12(alphabeta) units in the asymmetric unit was obtained by using (NH(4))(2)SO(4) as precipitant. These crystals diffract up to 2.8 A. Form II crystal obtained by using PEG4000 as precipitant belongs to space group P6(3) with unit cell constants a = 155.0 A, c = 40.3 A, gamma =120.0 degrees and one(alphabeta) unit in the asymmetric unit. The crystals diffract beyond 2.9 A. The possible stacking forms of phycocyanin molecules in the first crystal form were discussed.