BIOCHEMISTRY - Textbook - Ostapchenko L. I. - 2012

Chapter 10. NUCLEIC ACID METABOLISM

10.2. Digestion of Nucleic Acids in the Digestive Tract

Nucleic Acids (RNA and DNA) enter the body with food as Nucleoproteins. In The Stomach, they are denatured by Hydrochloric acid in gastric juice, causing the protein component to dissociate. The nucleic acids then undergo Hydrolysis mediated by endonuclease Enzymes (deoxyribonucleases and ribonucleases) of pancreatic juice (Fig. 10.3).

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Fig. 10.3. Nucleic acid Catabolism

Endonucleases hydrolyze phosphodiester bonds within polymeric DNA and RNA chains, yielding oligonucleotides. These are subsequently broken down by pancreatic phosphodiesterases into a mixture of 3'- and 5'-mononucleotides. Next, nucleotidases and nonspecific Phosphatases hydrolytically cleave the phosphate group from the NUCLEOTIDES, converting them into nucleosides. The breakdown of nucleic acids is completed by intestinal nucleosidases or nucleoside phosphorylases, which hydrolyze the bonds between nitrogenous bases and pentoses to release free purine and pyrimidine bases along with pentoses (ribose, deoxyribose).

If nucleosides and/or nitrogenous bases are not utilized in nucleotide Salvage Pathways, the majority of free purine bases in Cells—particularly in enterocytes—are oxidized by xanthine oxidase into uric acid, which is then excreted in the urine. Meanwhile, under the action of the intestinal microflora, pyrimidine bases are primarily degraded into CO2, NH3, β-Alanine, and β-aminoisobutyrate.