Porphyrin as an Ideal Biomarker in the Search for Extraterrestrial Life

Abstract

A key issue in astrobiological research is identifying target molecules that are unambiguously biological in origin and can be easily detected and recognized. We suggest porphyrin derivatives as an ideal target, because these chromophores are global in distribution and found in virtually all living organisms on Earth, including microorganisms that may approximate the early evolution of life on Earth. We discuss the inherent qualities that make porphyrin ideally suited for astrobiological research and discuss methods for detecting porphyrin molecules in terrestrial sedimentary environments. We present preliminary data to support the use of ToFSIMS as a powerful technique in the identification of porphyrins.

Hemoglobin-derived porphyrins preserved in a Middle Eocene blood-engorged mosquito

“…2 D and E). Comparison of the exact masses of analyzed peaks with the hemoglobin control and calculated masses of porphyrin derivatives (Table S1), as well as previous ToF-SIMS studies on heme, strongly indicate that the iron is still part of the porphyrin structure (25,(28)(29)(30). The most significant difference between the spectra of the female mosquito abdomen and the spectra of the purified pig hemoglobin is the absence of the peak for the intact heme ion [M] + at m/z 616.18 and the fragment ions centering at m/z 557.14, [M-CH 2 COOH] + .…”

“…Porphyrins are energetically very stable molecules and have been shown to be preserved through geological time as common components of many oil shales (28,29). Although the majority of such geoporphyrins are derived from chlorophyll and bacteriochlorophyll, some are thought to be derived from either heme or its precursors found in microbial cytochromes and related proteins.…”

“…As previously suggested, ToF-SIMS has significant potential for the unequivocal detection and nondestructive in situ localization of heme and related porphyrins in fossilized life forms (29). Although not readily applicable to amber inclusions, wider application of this technology to compression fossils may lead to the identification of other biomolecules and provide insight as to their heretofore unsuspected preservation.…”

Fundamental molecules of life are pigments which arose and co-evolved as a response to the thermodynamic imperative of dissipating the prevailing solar spectrum

“…In the context of the thermodynamic dissipation theory for the origin of life, this putative pigment-carrying membrane protein, instead of being an "ancient UV protector" is more appropriately designated as the "new generation" of UV-dissipating pigments, continuing, from the nucleic and aromatic amino acids, the thermodynamic role of photon dissipation and catalysis of the water cycle. Since porphyrin/chlorin-carrying proteins are universal to all three domains of life (Georgopapadakou and Scott, 1977;Suo et al, 2007), either as chlorophyll-carrying photosystems or heme-carrying cytochromes, it is quite plausible that this primordial porphyrin-protein complex was the main dissipating unit of the LUCA protocells.…”

The persistence of a chlorophyll spectral biosignature from Martian evaporite and spring analogues under Mars-like conditions

“…As such, it has been identified as a very detectable molecular biomarker (Parnell et al 2007), and has been characterized as a biosignature relevant to Mars (e.g., Vishnivetskaya et al 2003;Edwards et al 2004;Parnell 2005;Bishop et al 2006;Dartnell et al 2010;Gomez et al 2011). Additionally, the breakdown products of chlorophyll and porphyrins have been identified as stable and geologically persistent molecules (Baker & Louda 1986;Parnell et al 2007) that are detectable using a variety of methods (Suo et al 2007). While chlorophyll in exposed cyanobacteria is susceptible to degradation by ionizing radiation and loses is spectral properties (Dartnell et al 2011), the role of an endolithic niche and mineral shielding has yet to be explored with UV/VIS reflectance spectroscopy, as most work was focused on Raman and infrared (IR) spectroscopy (Wynn-Williams et al 2002;Marshall et al 2006;Pullan et al 2008;Foster et al 2010).…”