Nucleotides catabolism
The gastric enzymes do not act on the eaten nucleic acids. In the duodenum (small intestine) though, the enzymes ribonuclease and deoxyribonuclease I and II, excreted in the pancreatic juice, hydrolyze them to oligonucleotides. These are then hydrolyzed by phosphodiesterases, also excreted by the pancreas yielding 5' and 3'-mononucleotides. Many of them are dephosphorylated to nucleosides by diverse nucleotidases or by non-especific phosphatases. The resulting nucleosides can be absorbed by the intestinal mucosa or cleaved by nucleosidases - nucleoside phosphorilases ( acting on purines, pyrimidines, specific on uridine or thymine), yielding free bases.
The small intestine mucose is rich of nucleoside phosphorilases, so even the absorbed nucleosides will probably be hydrolyzed to free bases within the cell.
Nucleoside + Pi
base + ribose-1-P
Nucleoside + H2O
base + ribose
It's been shown that only small amounts of purines and pyrimidines from eaten nucleic acids are used to synthesize nucleic acids in the tissues. Most of the purines is degradated.
Schematically:
