Spectral Tuning in Biology

Björn, Lars Olof; Ghiradella, Helen

doi:10.1007/978-0-387-72655-7_9

Cited by 4 publications

(2 citation statements)

References 131 publications

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“…Spectral features of similar molecules can also change depending on the environment. For example, chlorophyll a has an absorption peak at 663 nm when diluted in acetone and in monomeric state (19). This peak is red-shifted in vivo to 680 nm and in some cases to even longer wavelengths, as high as 720 nm (20).…”

Section: Discussionmentioning

confidence: 99%

Surface biosignatures of exo-Earths: Remote detection of extraterrestrial life

Hegde

Paulino-Lima

Kent

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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Exoplanet discovery has made remarkable progress, with the first rocky planets having been detected in the central star's liquid water habitable zone. The remote sensing techniques used to characterize such planets for potential habitability and life rely solely on our understanding of life on Earth. The vegetation red edge from terrestrial land plants is often used as a direct signature of life, but it occupies only a small niche in the environmental parameter space that binds life on present-day Earth and has been widespread for only about 460 My. To more fully exploit the diversity of the one example of life known, we measured the spectral characteristics of 137 microorganisms containing a range of pigments, including ones isolated from Earth's most extreme environments. Our database covers the visible and near-infrared to the short-wavelength infrared (0.35-2.5 μm) portions of the electromagnetic spectrum and is made freely available from biosignatures. astro.cornell.edu. Our results show how the reflectance properties are dominated by the absorption of light by pigments in the visible portion and by strong absorptions by the cellular water of hydration in the infrared (up to 2.5 μm) portion of the spectrum. Our spectral library provides a broader and more realistic guide based on Earth life for the search for surface features of extraterrestrial life. The library, when used as inputs for modeling disk-integrated spectra of exoplanets, in preparation for the next generation of space-and ground-based instruments, will increase the chances of detecting life.biosignatures | spectral library | reflectivity | extremophiles | pigments I n the last decade, the field of exoplanet research has transitioned rapidly from detection to detection and characterization, with the first rocky exoplanets detected in the central star's liquid water habitable zone. Much of the excitement of this research in both the astrobiology community and the general public is motivated by the quest to discover a second genesis of life. The great distances that separate us from even the most nearby stars dictate that all measurements of the exoplanet must be made through remote sensing techniques for the foreseeable future. Thus, it is critical for us to determine the types of biosignatures that we should be looking for when designing the next generation of ground-and space-based instruments that will observe these planets at high spectral and possibly spatial resolutions.Since the mid-1960s a primary life-searching strategy has been to look for a specific combination of an oxidizing and a reducing gas in the exoplanetary atmosphere, such as the O 2 and CH 4 in our atmosphere, because this is a thermodynamically unstable situation suggesting that an active agent such as life is responsible for the chemical disequilibrium (1, 2). Of particular interest, both from an observational and modeling perspective, is to complement those indirect life detection studies with surface features that are direct properties of the organisms themselves (3).Alt...

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Section: Discussionmentioning

confidence: 99%

Surface biosignatures of exo-Earths: Remote detection of extraterrestrial life

Hegde

Paulino-Lima

Kent

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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“…For this reason, the chemical compounds that yield the toxic photochemical products on light exposure are regarded as phototoxins, categorized into two classes: radical-generating type 1 and singlet oxygen-generating type 2 phototoxins (1). Pigments with alternating single and double bonds absorb light at specific wavelengths through conjugated electron systems (2,3). Photoabsorbance by pigments is a prerequisite for photochemical reactions, but theoretical prediction of phototoxins among pigment molecules has been challenging (4).…”

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confidence: 99%

Analysis of phototoxin taste closely correlates nucleophilicity to type 1 phototoxicity

Ahn

Sung

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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Pigments often inflict tissue-damaging and proaging toxicity on light illumination by generating free radicals and reactive oxygen species (ROS). However, the molecular mechanism by which organisms sense phototoxic pigments is unknown. Here, we discover that Transient Receptor Potential Ankyrin 1-A isoform [TRPA1(A)], previously shown to serve as a receptor for free radicals and ROS induced by photochemical reactions, enables Drosophila melanogaster to aphotically sense phototoxic pigments for feeding deterrence. Thus, TRPA1(A) detects both cause (phototoxins) and effect (free radicals and ROS) of photochemical reactions. A group of pigment molecules not only activates TRPA1(A) in darkness but also generates free radicals on light illumination. Such aphotic detection of phototoxins harboring the type 1 (radical-generating) photochemical potential requires the nucleophile-sensing ability of TRPA1. In addition, agTRPA1(A) from malaria-transmitting mosquitoes Anopheles gambiae heterologously produces larger current responses to phototoxins than Drosophila TRPA1(A), similar to their disparate nucleophile responsiveness. Along with TRPA1(A)-stimulating capabilities, type 1 phototoxins exhibit relatively strong photo-absorbance and low energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. However, TRPA1(A) activation is more highly concordant to type 1 phototoxicity than are those photochemical parameters. Collectively, nucleophile sensitivity of TRPA1(A) allows flies to taste potential phototoxins for feeding deterrence, preventing postingestive photo-injury. Conversely, pigments need to bear high nucleophilicity (electron-donating propensity) to act as type 1 phototoxins, which is consistent with the fact that transferring photoexcited electrons from phototoxins to other molecules causes free radicals. Thus, identification of a sensory mechanism in Drosophila reveals a property fundamental to type 1 phototoxins.

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A viewpoint: Why chlorophyll a?

et al. 2009

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Chlorophyll a (Chl a) serves a dual role in oxygenic photosynthesis: in light harvesting as well as in converting energy of absorbed photons to chemical energy. No other Chl is as omnipresent in oxygenic photosynthesis as is Chl a, and this is particularly true if we include Chl a(2), (=[8-vinyl]-Chl a), which occurs in Prochlorococcus, as a type of Chl a. One exception to this near universal pattern is Chl d, which is found in some cyanobacteria that live in filtered light that is enriched in wavelengths >700 nm. They trap the long wavelength electronic excitation, and convert it into chemical energy. In this Viewpoint, we have traced the possible reasons for the near ubiquity of Chl a for its use in the primary photochemistry of Photosystem II (PS II) that leads to water oxidation and of Photosystem I (PS I) that leads to ferredoxin reduction. Chl a appears to be unique and irreplaceable, particularly if global scale oxygenic photosynthesis is considered. Its uniqueness is determined by its physicochemical properties, but there is more. Other contributing factors include specially tailored protein environments, and functional compatibility with neighboring electron transporting cofactors. Thus, the same molecule, Chl a in vivo, is capable of generating a radical cation at +1 V or higher (in PS II), a radical anion at -1 V or lower (in PS I), or of being completely redox silent (in antenna holochromes).

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Spectral Tuning in Biology

Cited by 4 publications

References 131 publications

Surface biosignatures of exo-Earths: Remote detection of extraterrestrial life

Surface biosignatures of exo-Earths: Remote detection of extraterrestrial life

Analysis of phototoxin taste closely correlates nucleophilicity to type 1 phototoxicity

A viewpoint: Why chlorophyll a?

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