Structural basis for the photochemistry of [alpha]-phycoerythrocyanin

The crystal structure of [alpha]-phycoerythrocyanin with its chromophore in the E-configuration is compared with the Z-configuration found in trimeric phycoerythrocyanin (PEC) to reveal the structural bases of the isomerization. The photochemistry in [alpha]-PEC is coupled to two regions, the H4-H5 and H7-H8 loops where large structural changes occur.