Changes

[[File:GeoWikiWriteOff2021-Aljezen-Figure3.jpg|framed|{{figure number|3}}shows the mechanism to activate hydrocarbons using Fumarate addition strategy.]]

[[File:GeoWikiWriteOff2021-Aljezen-Figure3.jpg|framed|{{figure number|3}}shows the mechanism to activate hydrocarbons using Fumarate addition strategy.]]

Oxygen-independent hydroxylation is another pathway that selected microbes can utilize to activate hydrocarbons in the absence of oxygen. This is illustrated below using ethylbenzene as an example (Figure 4). The process will start with the attack of a hydroxyl group (-OH) to the closest carbon atom to the ring with the help of ethylbenzene dehydrogenase enzyme, forming (S)-1-phenylethanol. Then a molecule of carbon dioxide will react with (S)-1-phenylethanol with the help of (S)-1-phenylethanol dehydrogenase enzyme to form benzoylacetate. The last two steps of the process involve reaction with a thiol group that contains co-enzyme A (CoA). The first thiol attack will convert benzoylacetate to benzoylacetyl-CoA. The second thiol attack will cleave the benzoylacetyl-CoA to benzoyl-CoA and acetyl-CoA (fig.4) [7][9][10][11].

Oxygen-independent hydroxylation is another pathway that selected microbes can utilize to activate hydrocarbons in the absence of oxygen. This is illustrated below using ethylbenzene as an example (Figure 4). The process will start with the attack of a hydroxyl group (-OH) to the closest carbon atom to the ring with the help of ethylbenzene dehydrogenase enzyme, forming (S)-1-phenylethanol. Then a molecule of carbon dioxide will react with (S)-1-phenylethanol with the help of (S)-1-phenylethanol dehydrogenase enzyme to form benzoylacetate. The last two steps of the process involve reaction with a thiol group that contains co-enzyme A (CoA). The first thiol attack will convert benzoylacetate to benzoylacetyl-CoA. The second thiol attack will cleave the benzoylacetyl-CoA to benzoyl-CoA and acetyl-CoA ([[:File:GeoWikiWriteOff2021-Aljezen-Figure4.jpg|Figure 4]]).<ref name="7Fuchsetal" /><ref name="9Heider">Heider, J., 2007, [https://www.sciencedirect.com/science/article/abs/pii/S1367593107000269?via%3Dihub Adding handles to unhandy substrates: Anaerobic hydrocarbon activation mechanisms]: Current Opinion in Chemical Biology, v. 11, no. 2, p. 188-194.</ref><ref name="10Bolletal">Boll, M., C. Loffler, B. E. Morris, and J. W. Kung, 2014, [https://sfamjournals.onlinelibrary.wiley.com/doi/10.1111/1462-2920.12328 Anaerobic degradation of homocyclic aromatic compounds via arylcarboxyl-coenzyme A esters: Organisms, strategies and key enzymes]: Environmental Microbiology, v. 6, no. 3, p. 612-627.</ref><ref name="11Callaghan">Callaghan, A. V., 2013, Enzymes involved in the anaerobic oxidation of ''n''-alkanes: From methane to long-chain paraffins: Frontiers in Microbiology, v. 4, article no. 89, 4 p.</ref>

[[File:GeoWikiWriteOff2021-Aljezen-Figure4.jpg|thumbnail| Figure 4 shows the mechanism to activate hydrocarbons using Oxygen-Independent Hydroxylation strategy.]]

[[File:GeoWikiWriteOff2021-Aljezen-Figure4.jpg|framed|{{Figure number|4}}shows the mechanism to activate hydrocarbons using Oxygen-Independent Hydroxylation strategy.]]

The third pathway is carboxylation. Carboxylation of non-branched alkyl chains the need of the presence of an alkyl group attached to it (e.g. benzene and naphthalene). The exact carboxylation reaction mechanism is still debated, but it is agreed that carbon dioxide is attached directly to the aromatic or aliphatic hydrocarbon via a carboxylase enzyme, requiring the presence of iron and nitrate reducing conditions [12].

The third pathway is carboxylation. Carboxylation of non-branched alkyl chains the need of the presence of an alkyl group attached to it (e.g. benzene and naphthalene). The exact carboxylation reaction mechanism is still debated, but it is agreed that carbon dioxide is attached directly to the aromatic or aliphatic hydrocarbon via a carboxylase enzyme, requiring the presence of iron and nitrate reducing conditions [12].

[8]  

[8]  

[9] Heider, J., 2007. Adding handles to unhandy substrates: anaerobic hydrocarbon activation mechanisms.

[9]  

[10] Boll, M., Loffler, C., Morris, B.E. and Kung, J.W., 2014. Anaerobic degradation of homocyclic aromatic compounds via arylcarboxyl-coenzyme A esters: organisms, strategies and key enzymes.

[10]  

[11] Callaghan, A.V., 2013. Enzymes involved in the anaerobic oxidation of n-alkanes: from methane to long-chain paraffins.

[11]  

[12] Biocatalytic carboxylation - Chemical Society Reviews (RSC Publishing)

[12] Biocatalytic carboxylation - Chemical Society Reviews (RSC Publishing)