Holophytochrome assembly. Coupled assay for phytochromobilin synthase in organello


Terry, M.J. and Lagarias, J.C. (1991) Holophytochrome assembly. Coupled assay for phytochromobilin synthase in organello. Journal of Biological Chemistry, 266, (33), 22215-2221. (PMID:1939244).

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Description/Abstract

Utilizing an in vitro coupled assay system, we show that isolated plastids from cucumber cotyledons convert the linear tetrapyrrole biliverdin IX alpha to the free phytochrome chromophore, phytochromobilin, which assembles with oat apophytochrome to yield photoactive holoprotein. The spectral properties of this synthetic phytochrome are indistinguishable from those of the natural photoreceptor. The plastid-dependent biliverdin conversion activity is strongly stimulated by both NADPH and ATP. Substitution of the nonnatural XIII alpha isomer of biliverdin for the IX alpha isomer affords a synthetic holophytochrome adduct with blue-shifted difference spectra. These results, together with experiments using boiled plastids, indicate that phytochromobilin synthesis from biliverdin is enzyme-mediated. Experiments where NADPH (and ATP) levels in intact developing chloroplasts are manipulated by feeding the metabolites 3-phosphoglycerate, dihydroxyacetone phosphate, and glucose 6-phosphate or by illumination with white light, support the hypothesis that the enzyme that accomplishes this conversion, phytochromobilin synthase, is plastid-localized. It is therefore likely that all of the enzymes of the phytochrome chromophore biosynthetic pathway reside in the plastid.

Item Type: Article
ISSNs: 0021-9258 (print)
1083-351X (electronic)
Related URLs:
Subjects: Q Science > QH Natural history > QH301 Biology
Q Science > QK Botany
Divisions: University Structure - Pre August 2011 > School of Biological Sciences
ePrint ID: 182713
Date Deposited: 18 May 2011 10:36
Last Modified: 27 Mar 2014 19:38
URI: http://eprints.soton.ac.uk/id/eprint/182713

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