Phytochrome assembly. The structure and biological activity of 2(R),3(E)-phytochromobilin derived from phycobiliproteins.


Cornejo, J., Beale, S.I., Terry, M.J. and Lagarias, J.C. (1992) Phytochrome assembly. The structure and biological activity of 2(R),3(E)-phytochromobilin derived from phycobiliproteins. Journal of Biological Chemistry, 267, (21), 14790-14798. (PMID:1634523).

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Description/Abstract

The unicellular rhodophyte, Porphyridium cruentum, and the filamentous cyanobacterium, Calothrix sp. PCC 7601, contain phycobiliproteins that have covalently bound phycobilin chromophores. Overnight incubation of solvent-extracted cells at 40 degrees C with methanol liberates free phycobilins that are derived from the protein-bound bilins by methanolytic cleavage of the thioether linkages between bilin and apoprotein. Two of the free bilins were identified as 3(E)-phycocyanobilin and 3(E)-phycoerythrombilin by comparative spectrophotometry and high pressure liquid chromatography. Methanolysis also yields a third bilin free acid whose absorption and 1H NMR spectra support the assignment of the 3(E)-phytochromobilin structure. This novel bilin is the major pigment isolated from cells that are pre-extracted with acetone-containing solvents. Since phytochrome- or phytochromobilin-containing proteins are not present in either organism, the 3(E)-phytochromobilin must arise by oxidation of phycobilin chromophores. This pigment is not obtained by similar treatment of a cyanobacterium and a rhodophyte that lack phycoerythrin. Therefore, 3(E)-phytochromobilin appears to be derived from phycoerythrobilin-containing proteins. Comparative CD spectroscopy of 3(E)-phytochrombilin and 3(E)-phycocyanobilin suggests that the two bilins share the R stereochemistry at the 2-position in the reduced pyrrole ring. Incubation of 2(R),3(E)-phytochromobilin with recombinant oat apophytochrome yields a covalent bilin adduct that is photoactive and spectrally indistinguishable from native oat phytochrome isolated from etiolated seedlings. These results establish that the phycobiliprotein-derived 2(R),3(E)-phytochromobilin is a biologically active phytochrome chromophore precursor.

Item Type: Article
ISSNs: 0021-9258 (print)
1083-351X (electronic)
Related URLs:
Subjects: Q Science > QH Natural history > QH301 Biology
R Medicine > R Medicine (General)
Divisions: University Structure - Pre August 2011 > School of Biological Sciences
ePrint ID: 182711
Date Deposited: 12 May 2011 10:51
Last Modified: 27 Mar 2014 19:38
URI: http://eprints.soton.ac.uk/id/eprint/182711

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