Which of the following is not true about hypoxanthineguanine phosphoribosyl transferase?
Predominantly present in liver
Involved in purine metabolism
PRPP is the substrate required
Its deficiency leads to Lysch Nyhan disease.
"SALVAGE REACTIONS" CONVE PURINES & THEIR NUCLEOSIDES TO MONONUCLEOTIDES Conversion of purines, their ribonucleosides, and their deoxyribonuc]eosides 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. * C/f: 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.