In the process of renewing the nucleic acid (especially RNA) of most cells, it is necessary to decompose the nucleic acid to produce nucleoside and free base. The process that cells use free bases or nucleosides to recombine corresponding nucleotides is called salvage pathway. Unlike the ab initio synthesis, the process of remedial synthesis is simpler and consumes less energy. Two enzymes with different specificity are involved in the recovery synthesis of purine nucleotides. Adenine phosphoribosyltransferase (aprt) catalyzes the synthesis of AMP from PRPP and adenine. The recovery synthesis of purine nucleoside in human body can only be catalyzed by adenosine kinase to make adenine nucleoside generate adenine nucleotide.
Purine nucleotide salvage synthesis is a secondary pathway. On the one hand, it can save energy and reduce the consumption of amino acids. On the other hand, it has important physiological significance for some tissues lacking the main synthetic pathway, such as human leukocytes and platelets, brain, bone marrow, spleen, etc. For example, seseh Nyhan syndrome is caused by severe genetic defects of HGPRT. The disease is a sex linked genetic defect found in men. The patients showed hyperuricemia and neurologic abnormalities. Such as brain hypoplasia, mental retardation, aggressive and destructive behavior, often bite their lips, hands and toes, it is also known as self destructiveness. The increase of uric acid is easy to explain. Due to the lack of HGPRT, PRPP produced by decomposition can not be utilized and piled up. PRPP promotes the de novo synthesis of purine, thus increasing uric acid, the decomposition product of purine. However, the mechanism of nervous system symptoms is not clear.