Abstract
In bacteria and eukaryotes, the pentose
moiety of nucleosides are degraded through the pentose
phosphate pathway. In contrast, since the pentose
phosphate pathway is absent in many archaea, it had not
been known how nucleosides are degraded in these
archaea. On the other hand, the NMP degradation
pathway, consisting of AMP phosphorylase,
ribose-1,5-bisphosphate isomerase and type III
ribulose-1,5-bisphosphate carboxylase/oxygenase, had
previously been identified in archaea. In the archaeon
Thermococcus kodakarensis, three nucleoside
phosphorylases and an ADP-dependent ribose-1-
phosphate kinase turned out to convert adenosine,
guanosine and uridine to ribose 1,5-bisphosphate,
whereas a cytidine kinase was suggested to
phosphorylate cytidine to CMP. Since these enzymes link
nucleosides to the previously identified NMP
degradation pathway, this metabolic network turned out
to link nucleosides to central carbon metabolism. In this
metabolic network, nucleosides are converted to ribose
1,5-bisphosphate and ribulose 1,5-bisphosphate as
intermediates, which is thus designated the pentose
bisphosphate pathway.
