Native R-phycoerythrin from Porphyra yezoensis has a molecular weight of 230, 000±23,000 dalton in 0.05 mol/L potassium phosphate at pH 7.5 and an absorption spectrum with the maxima at 565 and 498 nm and a shoulder at 540 nm, Its fluorescence emission maximum is at 578 nm in the above buffer. Single crystal X-ray diffraction investigation is in progress from R-phycoerythrin. It is crystallized in the rhombohedral space group R3 with a=b=187.5±2.5, c=60.0±3,0. The densities measured on the crystals and its mother liquor are 1.215 g/cm3 and 1.070 g/cm3 respectively. The fraction of the crystal volume occupied by the protein is 51.5%.It has been estimated that the ctystallographic asymmetric unit in rhombohedral lattice might contain （αβ）2 with a total molecular mass of less than 8×104 dalton. The hexagonal unit cell could accommodate three cylindrical molecules 108 in diameter and 60 in height, which is dictated by the space group symmetry for packing into the unit cell.
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