The native forms of the phycobilin chromophores of algal biliproteins. A clarification

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Abstract
Pigments released from phycoerythrins and phycocyanins by treatment with hot methanol are currently regarded as equivalent to the native chromophores phycoerythrobilin and phycocyanobilin. Evidence presented here confirms the original views of O''Carra and O''hEocha that these methanol-released pigments are artefacts differing in their chromophoric conjugated systems from the native protein-bound prosthetic groups. By contrast, the native spectral properties are retained in pigments released by careful acid treatment of the biliproteins and these acid-released phycobilins, rather than the methanol-released pigments, are therefore regarded as the protein-free forms of the native chromophores. The conclusion reached by Chapman, Cole and Siegelman, that all the algal [Rhodymenia palmata, Phormidium persicinum, Nostoc punctiforme, Ceramium rubrum and Hemiselmis virescens] biliproteins contain only phycoerythrobilin and phycocyanobilin, is shown to be incorrect. The identification of a urobilinoid chromophore, phycourobilin, accompanying phycoerythrobilin in B- and R-phycoerythrins is confirmed and supported by more extensive evidence. The cryptomonad phycocyanins contain a phycobilin chromophore accompanying phycocyanobilin. This further phycobilin has the spectral properties of the class of bilins known as violins and the provisional name cryptoviolin is proposed pending elucidation of its structure.