| 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] |
Hemoglycin (previously termed hemolithin) is a space polymer that is the first polymer of amino acids found in meteorites. [2] [3] [4]
Structural work has determined that its 1,494 Dalton core unit (Glycine 18 / Hydroxy-glycine 4 / 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]
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.
Hemoglycin is a completely abiotic molecule that forms in molecular clouds going on to protoplanetary disks, way 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.[ citation needed ] Potentially this fossil hemoglycin was delivered during the Late Heavy Bombardment (LHB) to Earth. Data to support this being the hemoglycin in the fossil has extraterrestrial isotopes similar to that in meteorites.
The polymer on the precambrian Earth could have functioned to drive the Great Oxygenation Event (GOE) beginning 2.4 Gya by splitting water in response to ultraviolet irradiation. Also, it could provide an energy source to early biochemistry and/or it simply delivered a source of polymer glycine.
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In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula CH3. In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in many organic compounds. It is a very stable group in most molecules. While the methyl group is usually part of a larger molecule, bounded to the rest of the molecule by a single covalent bond, it can be found on its own in any of three forms: methanide anion, methylium cation or methyl radical. The anion has eight valence electrons, the radical seven and the cation six. All three forms are highly reactive and rarely observed.
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Astrochemistry is the study of the abundance and reactions of molecules in the universe, and their interaction with radiation. The discipline is an overlap of astronomy and chemistry. The word "astrochemistry" may be applied to both the Solar System and the interstellar medium. The study of the abundance of elements and isotope ratios in Solar System objects, such as meteorites, is also called cosmochemistry, while the study of interstellar atoms and molecules and their interaction with radiation is sometimes called molecular astrophysics. The formation, atomic and chemical composition, evolution and fate of molecular gas clouds is of special interest, because it is from these clouds that solar systems form.
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In biochemistry, non-coded or non-proteinogenic amino acids are distinct from the 22 proteinogenic amino acids, which are naturally encoded in the genome of organisms for the assembly of proteins. However, over 140 non-proteinogenic amino acids occur naturally in proteins and thousands more may occur in nature or be synthesized in the laboratory. Chemically synthesized amino acids can be called unnatural amino acids. Unnatural amino acids can be synthetically prepared from their native analogs via modifications such as amine alkylation, side chain substitution, structural bond extension cyclization, and isosteric replacements within the amino acid backbone. Many non-proteinogenic amino acids are important:
This is a glossary of terms used in meteoritics, the science of meteorites.
Hemolithin is a proposed protein containing iron and lithium, of extraterrestrial origin, according to an unpublished preprint. The result has not been published in any peer-reviewed scientific journal. The protein was purportedly found inside two CV3 meteorites, Allende and Acfer-086, by a team of scientists led by Harvard University biochemist Julie McGeoch. The report of the discovery was met with some skepticism and suggestions that the researchers had extrapolated too far from incomplete data.
