The enzyme, found in cyanobacteria and red algae, catalyses the attachment of the phycobilin chromophore phycocyanobilin to cysteine 155 of the ¦Â subunits of the phycobiliproteins C-phycocyanin and phycoerythrocyanin. The numbering used here corresponds to the enzyme from?Anabaena, and could vary slightly in other organisms.