Hemoglycin
| Hemoglycin | ||
|---|---|---|
| (Glycine-containing space polymer of amino acids found in meteorites) | ||
 Hemoglycin was found in Acfer 086, an Allende meteorite similar to that pictured. | ||
| Function | unknown, although possibly able to split water to hydroxyl and hydrogen moieties[1] | |
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Hemoglycin (previously termed hemolithin) is a space polymer that is the first polymer of amino acids found in meteorites.[2][3][4]
Structure
[edit]Structural work has determined that its 1,494 Dalton core unit (Glycine18 / Hydroxy-glycine4 / Fe2O4) contains iron, but not lithium, leading to the more general term hemoglycin for these molecules.[1][5] The hemoglycin core contains a total of 22 glycine residues in an anti-parallel beta sheet chain that is terminated at each end by an iron atom plus two oxygens. Four of these glycine residues are oxidized to hydroxy-glycine with hydroxy groups (-OH) on the alpha carbon. This structure was determined by mass spectrometry of meteoritic solvent extracts[1][2][5] and has been confirmed in X-ray scattering by crystals of hemoglycin,[6] and also by optical absorption.[3] Crystals show a 480 nm characteristic absorption that can only exist when hydroxy-glycine residues have R chirality and are C-terminal bonded to iron.[6]
History
[edit]Because hemoglycin has now been found to be the dominant polymer of amino acids in 6 different meteorites (Allende,[7] Acfer 086, Efremovka, Kaba, Orgueil and Sutter's Mill), each time with the same structure, it has been proposed[3][6] that it is produced by a process of template replication. The measured 480 nm absorbance is larger than expected for a racemic distribution of R and S chirality in the hydroxy-glycine residues, indicating an R chirality excess in the polymer. Modeling of template replication that is assumed to depend on 480 nm absorption leads to an excess of R chirality and thus is consistent with this finding.
Significance
[edit]Hemoglycin is a completely abiotic molecule that forms in molecular clouds which go on to become protoplanetary disks, long before biochemistry on exoplanets like Earth begins. Hemoglycin via its glycine could seed an exoplanet (one able to support early biochemistry), but its main function appears to be the accretion of matter via formation of an extensive low-density lattice[6] in space in a protoplanetary disk. Besides being present in carbonaceous meteorites, hemoglycin has also been extracted and crystallized from a fossil stromatolite that formed on Earth 2.1 billion years ago.[8] Potentially this fossil hemoglycin was delivered to Earth during the Late Heavy Bombardment (LHB). Data to support this is that the hemoglycin in the fossil has extraterrestrial isotopes similar to that in meteorites.
The polymer on the precambrian Earth could have driven the Great Oxygenation Event (GOE) beginning 2.4 Gya by splitting water in response to ultraviolet irradiation. Also, it could have provided an energy source to early biochemistry and/or it could have simply delivered a source of polymer glycine.
See also
[edit]References
[edit]- ^ a b c McGeoch, Malcolm. W.; Dikler, Sergei; McGeoch, Julie E. M. (22 February 2020). "Hemolithin: a Meteoritic Protein containing Iron and Lithium". arXiv:2002.11688 [astro-ph.EP].
- ^ a b McGeoch, J.E.M.; McGeoch, M.W. (2015). "Polymer amide in the Allende and Murchison meteorites". Meteoritics & Planetary Science. 50 (12): 1971–1983. Bibcode:2015M&PS...50.1971M. doi:10.1111/maps.12558. S2CID 97089690.
- ^ a b c McGeogh, Julie E. M.; McGeogh, Malcolm W. (28 September 2022). "Chiral 480nm absorption in the hemoglycin space polymer: a possible link to replication". Scientific Reports. 12 (1): 16198. doi:10.1038/s41598-022-21043-4. PMC 9519966. PMID 36171277.
- ^ Staff (29 June 2021). "Polymers in meteorites provide clues to early solar system". Science Digest. Retrieved 9 January 2023.
- ^ a b McGeoch, M. W.; Dikler, S.; McGeoch, J.E.M. (21 February 2021). "Meteoritic Proteins with Glycine, Iron and Lithium". arXiv:2102.10700 [physics.chem-ph].
- ^ a b c d McGeoch, Julie E. M.; McGeoch, Malcolm W. (29 June 2021). "Structural Organization of Space Polymers". Physics of Fluids. 33 (6). doi:10.1063/5.0053302. S2CID 236281487.
- ^ Jujeczko, Pawel (2022). "Lessons learned from the examinations of Allende meteorite" (PDF). Acta Societatis Metheoriticae Polonorium. 13: 37–46. Retrieved 10 January 2023.
- ^ McGeoch, Julie E. M.; Frommelt, A. J.; Owen, R. L.; Cinque, Gianfelice; McClelland, Arthur; Lageson, David; McGeoch, M. W. (2023). "Fossil and present-day stromatolite ooids contain a meteoritic polymer of glycine and iron". arXiv:2309.17195 [physics.geo-ph].
