Note: a dashed line (without arrowheads) between two compound names is meant to imply that the two names are just different instantiations of the same compound -- i.e. one may be a specific name and the other a general name, or they may both represent the same compound in different stages of a polymerization-type pathway. This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: fatty acid α-oxidation
|Superclasses:||Degradation/Utilization/Assimilation → Fatty Acid and Lipids Degradation → Fatty Acids Degradation|
Expected Taxonomic Range: Embryophyta
Although β-oxidation is the major route for fatty acid degradation, fatty acids can also be subject to α- and ω-oxidation. In α-oxidation, a fatty acid is oxidized at the α-position (C-2) to give rise to a 2-hydroperoxy fatty acid. 2-hydroperoxy fatty acids are chemically unstable and are quickly converted to chain-shortened (by one carbon) fatty aldehydes through decarboxylation, or to 2-hydroxy fatty acids. The chain-shortened fatty aldehydes are further oxidized to free fatty acids which can enter the next round of α-oxidation.
The conversion of the intermediate 2(R)-hydroperoxy fatty acids to 2(R)-hydroxy fatty acids may be spontaneous or catalyzed by a peroxidase [Hamberg02]. The 70 kDa subunit of pea α-dioxygenase was shown possess such a peroxidase activity [Saffert00]. Similarly, the conversion of the chain-shortened aldehydes to corresponding fatty acids may be spontaneous or catalyzed by a NAD+ oxidoreductase. The 50 kDa subunit of pea α-dioxygenase was shown to have an aldehyde dehydrogenase activity with NAD+. Both polysaturated and unsaturated fatty acids are effective substrates in the pathway. Among the tested ones are laurate, palmitate, stearate, oleate, linoleate, linolenate, and arachidonate.
In animal and human, α-oxidation is important to degrade β-methyl branched fatty acids which cannot be degraded through β-oxidation. The physiological role of fatty acid α-oxidation in plants is not clear. It is expected to be involved in chlorophyll/phytol degradation. It has also been suggested that the pathway may be related to seed germination (in the case of pea where α-dioxygenase is induced only during seed germination [Saffert00]) and plant response to wounding and plant-pathogen interactions (in the case of tobacco and Arabidopsis where α-dioxygenase is induced upon pathogen attack [Hamberg03][De02a]).
Unification Links: AraCyc:PWY-2501
De02a: De Leon IP, Sanz A, Hamberg M, Castresana C (2002). "Involvement of the Arabidopsis alpha-DOX1 fatty acid dioxygenase in protection against oxidative stress and cell death." Plant J 29(1);61-2. PMID: 12060227
Hamberg03: Hamberg M, Sanz A, Rodriguez MJ, Calvo AP, Castresana C (2003). "Activation of the fatty acid alpha-dioxygenase pathway during bacterial infection of tobacco leaves. Formation of oxylipins protecting against cell death." J Biol Chem 278(51);51796-805. PMID: 14522973
Hamberg99: Hamberg M, Sanz A, Castresana C (1999). "alpha-oxidation of fatty acids in higher plants. Identification of a pathogen-inducible oxygenase (piox) as an alpha-dioxygenase and biosynthesis of 2-hydroperoxylinolenic acid." J Biol Chem 274(35);24503-13. PMID: 10455113
Saffert00: Saffert A, Hartmann-Schreier J, Schon A, Schreier P (2000). "A dual function alpha-dioxygenase-peroxidase and NAD(+) oxidoreductase active enzyme from germinating pea rationalizing alpha-oxidation of fatty acids in plants." Plant Physiol 123(4);1545-52. PMID: 10938370
Liu04b: Liu W, Rogge CE, Bambai B, Palmer G, Tsai AL, Kulmacz RJ (2004). "Characterization of the heme environment in Arabidopsis thaliana fatty acid alpha-dioxygenase-1." J Biol Chem 279(28);29805-15. PMID: 15100225
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