15-16-dihydrobiliverdin-ixa and phycocyanobilin

Structures of the open-chain tetrapyrrole (bilin) prosthetic groups of the cryptophycean biliproteins phycocyanin 645 (Cr-PC 645; from strain UW374), phycoerythrin 566 (Cr-PE 566; from strain Bermani) and phycoerythrin 545 (Cr-PE 545; from Proteomonas sulcata Hill & Wetherbee) were examined by absorption, 1H NMR spectroscopy, and mass spectrometry. These biliproteins carry the following covalently attached bilins: Cr-PC 645 (alpha subunit) has one mesobiliverdin, (beta subunit), two phycocyanobilins and a doubly linked 15,16-dihydrobiliverdin; Cr-PC 566 (alpha), bilin 584, (beta), phycoerythrobilin and two bilin 584 chromophores (Wedemayer, G.J., Wemmer, D.E., and Glazer, A.N. (1991) J. Biol. Chem. 266, 4731-4741); Cr-PE 545 (alpha) has one 15,16-dihydrobiliverdin and (beta), only phycoerythrobilins. This is the first report of naturally occurring biliproteins carrying either 15,16-dihydrobiliverdin or mesobiliverdin chromophores. Native cryptomonad phycobiliproteins have been classified on the basis of the position of their long wavelength absorption maxima. However, comparison of the bilins of Cr-PE 566 from strain Bermani with those of Cr-PE 566 of strain CBD shows that the two proteins carry different bilins on the alpha subunit. Consequently, the identity of the bilin prosthetic groups on cryptophycean phycobiliproteins cannot be unambiguously inferred from simple inspection of the visible absorption spectra.

Topics: Biliverdine; Chromatography, Liquid; Eukaryota; Magnetic Resonance Spectroscopy; Mass Spectrometry; Molecular Structure; Phycobilins; Phycocyanin; Pyrroles; Spectrophotometry, Ultraviolet; Tetrapyrroles

A partially purified protein fraction from the phycocyanin-containing unicellular rhodophyte, Cyanidium caldarium, reductively transforms biliverdin IX alpha to a violet colored bilin in the presence of NADPH, ferredoxin, and ferredoxin-NADP+ reductase. This bilin has a violin-like absorption spectrum with maxima at 335 and 560 nm in methanolic HCl and at 337, 567, and 603-604 nm in CHCl3. The bilin has been determined to be 15,16-dihydrobiliverdin IX alpha by comparative spectrophotometry and 1H NMR spectroscopy. This product of biliverdin IX alpha reduction is converted enzymatically to phycobilins by further reduction. A general biosynthetic pathway is proposed which accounts for the formation of the phycobilins from biliverdin IX alpha by a two-step reduction process followed by isomerization.

Topics: Biliverdine; Chromatography, Gel; Magnetic Resonance Spectroscopy; Molecular Structure; Oxidation-Reduction; Phycobilins; Phycocyanin; Pyrroles; Rhodophyta; Spectrophotometry; Tetrapyrroles