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Pathway: periplasmic NAD degradation

Biochemical pathways in S. cerevisiae are manually curated and maintained in the YeastPathways database. This page summarizes the genes, enzymes, and metabolites involved in the pathway, along with the curated literature.

Pathway Name
periplasmic NAD degradation
Pathway ID
PERIPLASMA-NAD-DEGRADATION
SGD ID
SGD:S000249659
Genes
NPY1
Chemical Compounds
NAD(1-) | NMN(-) | adenosine | adenosine 5'-monophosphate(2-) | hydrogenphosphate | hydron | water

Pathway Diagram

Diagram of the pathway from YeastPathways. Click "View interactive diagram at YeastPathways" for the zoomable, clickable version.

periplasmic NAD degradation pathway diagram

View interactive diagram at YeastPathways

Pathway Summary

In some organisms, the metabolism of extracellular nicotinamide adenine dinucleotide (NAD+) plays an important role in purine salvage and uptake. In humans, for instance, extracellular NAD+ generated via cell lysis or other means can be salvaged for adenine through the following steps: 1) cleavage of NAD+ to AMP and nicotinamide mononucleotide (NMN) by NAD+ pyrophosphatase, 2) cleavage of AMP to release adenosine via 5-nucleotidase, 3) transport of extracellular adenosine into the cell via adenosine transporters, and 4) regeneration of adenine nucleotides from adenosine via phosphorylation. This process has been implicated human immune cell activation.

Extracellular metabolism of NMN, but not NAD+, is known to occur in S. cerevisiae. This occurs via Pho5p, the major secreted acid phosphatase in yeast. Pho5p catalyzes the conversion of exogenous NMN in the periplasm to nicotinamide riboside (NR), a NAD+ precursor that can be imported into the cell and converted back to NAD+ via salvage pathways. Deletion of PHO5 prevents growth of a mutant disrupted in the NAD+ biosynthesis pathway on medium containing NMN. In addition to Pho5p, two other enzymes are known to play a role in catabolizing extracellular nucleotides in S. cerevisiae: the nucleotide pyrophosphatasesphosphodiesterases Npp1p and Npp2p. Both yeast enzymes belong to a superfamily of alkaline phosphatases that also includes extracellular 5-nucleotidases from mammals.

Genes Involved

Genes whose products participate in this pathway, with their systematic names, EC numbers (where the gene product is an enzyme with an assigned EC number), and the gene's SGD description.

GeneSystematic NameEC NumberDescription
NPY1 YGL067W 3.6.1.22 NADH diphosphatase (pyrophosphatase)

Functional Networks

Functional Networks show how the genes in this pathway work together: a graph linking the pathway to its genes and their shared GO biological-process terms and phenotype observables, and the GO-CAM causal activity models that involve these genes.

Shared Annotations

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GO-CAMs

GO-CAM (Gene Ontology Causal Activity Model) pathway models that involve the genes in this pathway. A gene can participate in more than one model, so use the dropdown to switch between them; the model for this pathway is shown by default.

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GO Enrichment

Gene Ontology biological-process terms enriched among the genes in this pathway, computed with GO Term Finder. Terms are shown with the number of pathway genes annotated to them and the corrected p-value.

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References

List of references used specifically to curate the information on this page.

Resources

YeastPathways