Abstract: The bleaching of the monomers and the separated α and β subnits of R-phycoery-thrin from Polysiphonia urceolata by Cu²⁺, Cd²⁺, has been investigated. Upon the addition of Cu²⁺ and Cd²⁺, the visible absorption bands of the monomers at 496, 538 and 564 nm of R-phycoerythrin was bleached. The change in absorption induced by Cu²⁺ or Cd²⁺ was accompanied by a decreased fluorescence emission intensity. The bleaching capacity of Cu²⁺ is greater than that of Cd²⁺. When monomers and α subunit are bleached by Cu²⁺, there is no appearance of the characteristic absorption of chromophore complex at 648 nm. But this absorption appeares obviously in the case of β subunit. From above results, we conclude the mechanism is that the bleachng of monomers and α subunit is caused by the interaction of Cu²⁺ or Cd²⁺ with the residues of polypeptides, but β subunit is bleached by both of the interaction of Cu²⁺ or Cd²⁺ with residues of polypeptides and the coordination of Cu²⁺ or Cd²⁺ with chromophores.

Key words: bleaching, monomer of R-phycoerythrin, subunit of R-phycoerythrin, residue of polypeptide, chromophore complex