Catabolism of pyrimidine nucleotides in the deep-sea tube worm Riftia pachyptila.
The present study describes the distribution and properties of enzymes of the catabolic pathway of pyrimidine nucleotides in Riftia pachyptila, a tubeworm living around deep-sea hydrothermal vents and known to be involved in a highly specialized symbiotic association with a bacterium. The catabolic enzymes, 5'-nucleotidase, uridine phosphorylase, and uracil reductase, are present in all tissues of the worm, whereas none of these enzymatic activities were found in the symbiotic bacteria. The 5'-nucleotidase activity was particularly high in the trophosome, the symbiont-harboring tissue. These results suggest that the production of nucleosides in the trophosome may represent an alternative source of carbon and nitrogen for R. pachyptila, because these nucleosides can be delivered to other parts of the worm. This process would complement the source of carbon and nitrogen from organic metabolites provided by the bacterial assimilatory pathways. The localization of the enzymes participating in catabolism, 5'-nucleotidase and uridine phosphorylase, and of the enzymes involved in the biosynthesis of pyrimidine nucleotides, aspartate transcarbamylase and dihydroorotase, shows a non-homogeneous distribution of these enzymes in the trophosome. The catabolic enzymes 5'-nucleotidase and uridine phosphorylase activities increase from the center of the trophosome to its periphery. In contrast, the anabolic enzymes aspartate transcarbamylase and dihydroorotase activities decrease from the center toward the periphery of the trophosome. We propose a general scheme of anatomical and physiological organization of the metabolic pathways of the pyrimidine nucleotides in R. pachyptila and its bacterial endosymbiont.
Minic
Zoran
Z
Laboratoire de Biochimie des Signaux Régulateurs Cellulaires et Moléculaires, UMR 7631, CNRS, Université Pierre et Marie Curie, 96 Boulevard Raspail F-75006 Paris, France.
Pastra-Landis
Styliani
S
Gaill
Francoise
F
Hervé
Guy
G
D015720:5'-Nucleotidase / Q000378:metabolism; D000818:Animals; D002852:Chromatography, Ion Exchange; D003570:Cytidine Triphosphate / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D011077:Polychaeta / Q000378:metabolism*; D011742:Pyrimidine Nucleotides / Q000378:metabolism*; D013379:Substrate Specificity; D013559:Symbiosis
D011742:Pyrimidine Nucleotides; D003570:Cytidine Triphosphate; D015720:5'-Nucleotidase