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: ureide degradation
|Superclasses:||Degradation/Utilization/Assimilation → Amines and Polyamines Degradation → Allantoin Degradation|
Expected Taxonomic Range: Viridiplantae
Note: This is a chimeric pathway, comprising reactions from multiple organisms, and typically will not occur in its entirety in a single organism. The taxa listed here are likely to catalyze only subsets of the reactions depicted in this pathway.
The ureides allantoin and allantoate are the major nitrogenous compounds synthesized in root nodules of ureide exporting legumes, such as soybean, during nitrogen fixation. Synthesized ureides are transported from root nodules via the xylem to shoots, where they are rapidly degraded. The products of ureide catabolism are re-assimilated and utilized in nitrogen metabolism.
Early reports about allantoin degradation in Glycine max found that different cultivars were utilizing different routes [Winkler85, Shelp85, Winkler87, Winkler88, Vadez00]. However, a later study concluded that the previous investigations may have been misled by side effects of the enzyme inhibitor used, and that both cultivars were utilizing the same degradation pathway. In both cases the route from allantoate to S-ureidoglycolate involved the production of ammonia, while urea was produced later in the pathway, by ureidoglycolate urea-lyase (EC 18.104.22.168) [Todd04]. The later activity was also described in Cicer arietinum (chickpea), an amide transporter [Munoz01]. These conclusions were supported by the isolation of allantoate amidohydrolase and ureidoglycolate amidohydrolase from Phaseolus vulgaris [Raso07, Munoz06].
On the other hand, a conflicting report of ammonia-producing conversion of S-ureidoglycolate to glyoxylate by ureidoglycolate amidohydrolase (EC 22.214.171.124) in Phaseolus vulgaris has been reported [Wells91].
Complicating things further, an allantoicase (EC 126.96.36.199) has been purified from the green alga Chlamydomonas reinhardtii, suggesting the existence of additional allantoin degradation routes in green algae [Piedras00].
There is some uncertainty about the ureide degradation pathway in nitrogen fixing plants, since several routes are possible. The general scheme of the pathway is the degradation of (S)-(+)-allantoin via allantoate to S-ureidoglycolate, which is degraded futher into glyoxylate.
However, there are two possible routes leading from allantoate to S-ureidoglycolate, and there are two possible routes from S-ureidoglycolate to glyoxylate: each of these two steps can be performed by enzyme(s) that liberate the nitrogen as either ammonia or urea.
The ammonia-producing enzymes are allantoate amidohydrolase (EC 188.8.131.52), which converts allantoate to S-ureidoglycolate via a (-)-ureidoglycine, and ureidoglycolate amidohydrolase (EC 184.108.40.206), which converts S-ureidoglycolate to glyoxylate.
The urea-producing enzymes are allantoicase (EC 220.127.116.11), which converts allantoate directly to S-ureidoglycolate, and ureidoglycolate urea-lyase (EC 18.104.22.168), which converts S-ureidoglycolate to glyoxylate.
Subpathways: allantoin degradation to ureidoglycolate II (ammonia producing) , allantoin degradation to glyoxylate I , allantoin degradation to glyoxylate II , urea degradation II , allantoin degradation to ureidoglycolate I (urea producing)
Unification Links: AraCyc:URDEGR-PWY
Munoz01: Munoz A, Piedras P, Aguilar M, Pineda M (2001). "Urea Is a Product of Ureidoglycolate Degradation in Chickpea. Purification and Characterization of the Ureidoglycolate Urea-Lyase." Plant Physiol 2001;125(2);828-834. PMID: 11161040
Munoz06: Munoz A, Raso MJ, Pineda M, Piedras P (2006). "Degradation of ureidoglycolate in French bean (Phaseolus vulgaris) is catalysed by a ubiquitous ureidoglycolate urea-lyase." Planta 224(1);175-84. PMID: 16333637
Piedras00: Piedras P, Munoz A, Aguilar M, Pineda M (2000). "Allantoate amidinohydrolase (Allantoicase) from Chlamydomonas reinhardtii: its purification and catalytic and molecular characterization." Arch Biochem Biophys 378(2);340-8. PMID: 10860551
Piedras95: Piedras, P, Cardenas, J, Pineda, M (1995). "Solubilization and extraction of allantoinase and allantoicase from the green alga Chlamydomonas reinhardtii." Phytochemical Analysis.6(5):239-243.
Pineda94: Pineda M, Piedras P, Cardenas J (1994). "A continuous spectrophotometric assay for ureidoglycolase activity with lactate dehydrogenase or glyoxylate reductase as coupling enzyme." Anal Biochem 222(2);450-5. PMID: 7864371
Raso07: Raso MJ, Munoz A, Pineda M, Piedras P (2007). "Biochemical characterisation of an allantoate-degrading enzyme from French bean (Phaseolus vulgaris): the requirement of phenylhydrazine." Planta 226(5);1333-42. PMID: 17594111
Winkler88: Winkler RG, Blevins DG, Randall DD (1988). "Ureide Catabolism in Soybeans : III. Ureidoglycolate Amidohydrolase and Allantoate Amidohydrolase Are Activities of an Allantoate Degrading Enzyme Complex." Plant Physiol 86(4);1084-1088. PMID: 16666035
Benoit07: Benoit SL, Mehta N, Weinberg MV, Maier C, Maier RJ (2007). "Interaction between the Helicobacter pylori accessory proteins HypA and UreE is needed for urease maturation." Microbiology 153(Pt 5);1474-82. PMID: 17464061
Chen96c: Chen YY, Clancy KA, Burne RA (1996). "Streptococcus salivarius urease: genetic and biochemical characterization and expression in a dental plaque streptococcus." Infect Immun 1996;64(2);585-92. PMID: 8550211
Cusa99: Cusa E, Obradors N, Baldoma L, Badia J, Aguilar J (1999). "Genetic analysis of a chromosomal region containing genes required for assimilation of allantoin nitrogen and linked glyoxylate metabolism in Escherichia coli." J Bacteriol 1999;181(24);7479-84. PMID: 10601204
Kim00a: Kim GJ, Lee DE, Kim HS (2000). "Functional expression and characterization of the two cyclic amidohydrolase enzymes, allantoinase and a novel phenylhydantoinase, from Escherichia coli." J Bacteriol 2000;182(24);7021-8. PMID: 11092864
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