<prompt> Which of the following is not true about hypoxanthineguanine phosphoribosyl transferase?Predominantly present in liverInvolved in purine metabolismPRPP is the substrate requiredIts deficiency leads to Lysch Nyhan disease.  <response>: SALVAGE REACTIONS CONVE PURINES THEIR NUCLEOSIDES TO MONONUCLEOTIDES Conversion of purines, their ribonucleosides, and their deoxyribonuceosides to mononucleotides involves so- called salvage reactions that require far less energy than de novo synthesis. The more impoant mechanism involves phosphoribosylation by PRPP of a free punine Pu to form a purine 5-mononucleotide Pu-RP. Three processes contribute to purine nucleotide biosynthesis. These are, in order of decreasing impoance: 1 Synthesis from amphibolic intermediates synthesis de novo, 2 Phosphoribosyltion of purines, and 3 Phosphorylation of purine nucleosides. Lesch-Nyhan Syndrome X-linked recessive. Overproduction hyperuricemia. Purine salvage problem owing to absence of HGP, which conves hypoxanthine to IMP and guanine to GMP. Cf: o Mental retardation, o Self-mutilation, aggression, o Hyperuricemia, gout, and o Choreoathetosis. Reflects a defect in hypoxanthine-guanine phosphoribosyl transferase HGPase, an enzyme of purine salvage. The accompanying rise in intracellular PRPP results in purine overproduction. Mutations that decrease or abolish hypoxanthine-guanine phosphoribosyl transferase activity include deletions, frame-shift mutations, base substitutions, and aberrant mRNA splicing. 