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adenosine nucleotides degradation IV

General Background The distinction between nucleoside degradation and salvage is not always straight forward. A general rule is that degradation pathways start with the nucleotide forms and convert them to simpler forms, eventually leading to complete mineralization, while salvage pathways start with either the nucleoside or the free base form, and convert those to the nucleotide forms. Nucleotide recycling is achieved by a combination of both types - a nucleotide is partially degraded via a degradation pathway, but the products are shuttled into a salvage pathway rather then towrds complete mineralization. About This Pathway Type III RubisCO enzymes, capable of fixing |FRAME: CARBON-DIOXIDE| into |FRAME: D-RIBULOSE-15-P2|, are commonly found in archaebacteria. The importance of carbon fixation in these organisms has been unclear, though, since there seemed to be no obvious way for the organisms to replenish the substrate for these enzymes. The enzyme that generates |FRAME: D-RIBULOSE-15-P2| in organisms that contain the |FRAME:CALVIN-PWY|, |FRAME:PRKSYN-MONOMER|, is missing from almost all archaebacteria. A new route for the synthesis of |FRAME: D-RIBULOSE-15-P2| has been discovered in some archaebacteria, which involves an isomerization reaction from |FRAME:RIBOSE-15-BISPHOSPHATE|, catalyzed by |FRAME:MONOMER-13273|. In the hyper thermophile |FRAME: TAX-311400| it was shown that |FRAME:RIBOSE-15-BISPHOSPHATE| is produced from |FRAME:AMP| by the enzyme |FRAME:MONOMER-13274| |CITS: [17303759]|. In the methanogen |FRAME: TAX-2190|, on the other hand, it has been shawn that |FRAME:RIBOSE-15-BISPHOSPHATE| is produced from |FRAME: PRPP| |CITS: [15375115]|. Thus it seems that archaebacteria possess different pathways for RubisCO-mediated carbon fixation, in which the enzyme's substrate is generated by either salvage of |FRAME: AMP|, or by production from |FRAME: PRPP|, which can be produced from |FRAME:RIBOSE-5P|, an intermediate of the |FRAME:PENTOSE-P-PWY| |CITS: [17621634]|.

from BIOCYC source record: META_PWY-5532
Type: pathway
Taxonomic scope
conserved biosystem

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