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Pathway Description
Pentose Interconversion
Danio rerio
Metabolic Pathway
Pentoses are monosaccharides consisting of five carbon atoms with either aldehyde or ketone functional groups. There are eight stereoisomers of aldopentoses, which include arabinose, lyxose, ribose and xylulose, both D- and L- forms, while there are four for 2-ketopentoses, ribulose and xylulose. Ribose is also very biologically important, as it is one of the three parts of RNA, the others being the phosphate and bases, as well as being related to deoxyribose, one of the major constituents of DNA.
In this pathway, CDP-ribitol, the alcohol of pentose with an attached CDP, can be converted to and from D-ribitol 5-phosphate by D-ribitol-5-phosphate cytidylyltransferase, either adding a diphosphate group and removing CTP, or adding CTP and removing the diphosphate. D-ribitol 5-phosphate can then be converted to and from D-ribulose 5-phosphate by ribitol 5-phosphate dehydrogenase, which removes or adds a hydrogen. The protein making up this enzyme is currently unknown in Danio rerio.
D-ribulose 5-phosphate can be used in the pentose phosphate pathway, and it can also come from that pathway. It is converted to and from xylulose 5-phosphate by ribulse-phosphate 3-epimerase, and then a phosphate can be removed by xylulokinase to form D-xylulose in another two-way reaction. D-xylulose can then be converted to D-xylitol by sorbitol dehydrogenase, and D-xylitol can be converted to and from D-xylose by an aldehyde reductase. D-xylose can also come into this pathway from starch and sucrose metabolism, and can finally be converted to D-xylono-1,5-lactone by trans-1,2-dihydrobenzene-1,2-diol dehydrogenase, forming one of the end products of this pathway.
D-xylitol can also be conveted to and from L-threo-2-pentulose, also known as L-xylulose, by dicarbonyl/L-xylulose reductase, after which the L-thre-2-pentulose can be converted to and from L-arabitol by L-arabinitol 4-dehydrogenase, whose protein is also unknown in Danio rerio. Finally, L-arabitol can be converted to and from L-arabinose by aldose reductase, and L-arabinose can be used in either ascorbate and aldarate metabolism or amino sugar and nucleotide sugar metabolisms, and can also come from ascorbate and aldarate metabolism.
References
Pentose Interconversion References
Yew WS, Gerlt JA: Utilization of L-ascorbate by Escherichia coli K-12: assignments of functions to products of the yjf-sga and yia-sgb operons. J Bacteriol. 2002 Jan;184(1):302-6.
Pubmed: 11741871
Yew WS, Akana J, Wise EL, Rayment I, Gerlt JA: Evolution of enzymatic activities in the orotidine 5'-monophosphate decarboxylase suprafamily: enhancing the promiscuous D-arabino-hex-3-ulose 6-phosphate synthase reaction catalyzed by 3-keto-L-gulonate 6-phosphate decarboxylase. Biochemistry. 2005 Feb 15;44(6):1807-15. doi: 10.1021/bi047815v.
Pubmed: 15697206
Yasueda H, Kawahara Y, Sugimoto S: Bacillus subtilis yckG and yckF encode two key enzymes of the ribulose monophosphate pathway used by methylotrophs, and yckH is required for their expression. J Bacteriol. 1999 Dec;181(23):7154-60.
Pubmed: 10572115
Ibanez E, Gimenez R, Pedraza T, Baldoma L, Aguilar J, Badia J: Role of the yiaR and yiaS genes of Escherichia coli in metabolism of endogenously formed L-xylulose. J Bacteriol. 2000 Aug;182(16):4625-7.
Pubmed: 10913097
Orita I, Yurimoto H, Hirai R, Kawarabayasi Y, Sakai Y, Kato N: The archaeon Pyrococcus horikoshii possesses a bifunctional enzyme for formaldehyde fixation via the ribulose monophosphate pathway. J Bacteriol. 2005 Jun;187(11):3636-42. doi: 10.1128/JB.187.11.3636-3642.2005.
Pubmed: 15901685
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