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The Keto–Enol Tautomerism of Biliverdin in Bacteriophytochrome: Could it Explain the Bathochromic Shift in the Pfr Form?

Villegas-Escobar, Nery and Matute, Ricardo A. (2021) The Keto–Enol Tautomerism of Biliverdin in Bacteriophytochrome: Could it Explain the Bathochromic Shift in the Pfr Form? Photochemistry and Photobiology, 97 (1). pp. 99-109. ISSN 0031-8655. https://resolver.caltech.edu/CaltechAUTHORS:20201015-152734549

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Abstract

Phytochromes are ubiquitous photoreceptors found in plants, eukaryotic algae, bacteria and fungi. Particularly, when bacteriophytochrome is irradiated with light, a Z‐to‐E (photo)isomerization takes place in the biliverdin chromophore as part of the Pr‐to‐Pfr conversion. This photoisomerization is concomitant with a bathochromic shift in the Q‐band. Based on experimental evidence, we studied a possible keto–enol tautomerization of BV, as an alternative reaction channel after its photoisomerization. In this contribution, the noncatalyzed and water‐assisted reaction pathways for the lactam–lactim interconversion through consecutive keto–enol tautomerization of a model BV species were studied deeply. It was found that in the absence of water molecules, the proton transfer reaction is unable to take place at normal conditions, due to large activation energies, and the endothermic formation of lactim derivatives prevents its occurrence. However, when a water molecule assists the process by catalyzing the proton transfer reaction, the activation free energy lowers considerably. The drastic lowering in the activation energy for the keto–enol tautomerism is due to the stabilization of the water moiety through hydrogen bonds along the reaction coordinate. The absorption spectra were computed for all tautomers. It was found that the UV–visible absorption bands are in reasonable agreement with the experimental data. Our results suggest that although the keto–enol equilibrium is likely favoring the lactam tautomer, the equilibrium could eventually be shifted in favor of the lactim, as it has been reported to occur in the dark reversion mechanism of bathy phytochromes.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1111/php.13341DOIArticle
ORCID:
AuthorORCID
Villegas-Escobar, Nery0000-0002-6370-617X
Matute, Ricardo A.0000-0002-0644-3799
Additional Information:© 2020 The American Society of Photobiology. Issue Online: 24 January 2021; Version of Record online: 10 January 2020; Accepted manuscript online: 14 October 2020; Manuscript accepted: 08 October 2020; Manuscript received: 30 April 2020. The authors acknowledge financial support from FONDECYT Grant No. 1181260. Powered@NLHPC: This research was partially supported by the supercomputing infrastructure of the NLHPC (ECM‐02).
Funders:
Funding AgencyGrant Number
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1181260
Issue or Number:1
Record Number:CaltechAUTHORS:20201015-152734549
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20201015-152734549
Official Citation:Villegas‐Escobar, N. and Matute, R.A. (2021), The Keto–Enol Tautomerism of Biliverdin in Bacteriophytochrome: Could it Explain the Bathochromic Shift in the Pfr Form?†. Photochem Photobiol, 97: 99-109. https://doi.org/10.1111/php.13341
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106103
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:16 Oct 2020 14:55
Last Modified:28 Jan 2021 22:19

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