Purification, crystallization and preliminary x-ray analysis of a phycourobilin-containing phycoerythrin

Abstract: Rhodophycean phycoerythrin (R-PE) was isolated from the red alga Griffithsia monilis and purified on Q­ Sepharose. Untwinned crystals diffracting to 2.lA on a rotating anode X-ray source were obtained by the hanging-drop vapour diffusion method, and their space group determined as R3. SDS gel-electrophoresis of dissolved crystals showed the a and p subunits of the protein (apparent molecular weight, about 19 kDa) and two different forms of they-subunit (apparent molecular weight, 28 and 30 kDa) being present in the crystals.