Metabolism Of Purine

METABOLISM OF PURINE


METABOLISM OF PURINE

  • Purine nucleotides are synthesized-
  1. Adenosine monophosphate (AMP)
  2. Guanosine monophosphate (GMP)
  • Purine nucleotides synthesized by 2 pathways-
  1. De novo synthesis
  2. Salvage pathway

De novo synthesis

  • It is synthesis in liver.
  • It takes place in cytoplasm.
  • Precursors for de novo synthesis are –
  1. Glycine provides C4, C5 and N7
  2. Aspartate provides N1
  3. Glutamine provides N3 and N9
  4. Tetrahydrofolate derivatives furnish C2 and C8
  5. Carbon dioxide provides C6
  • IMP (also called inosinic acid) is the first purine nucleotide, which is synthesized as the precursor of AMP (also called adenylic acid) and GMP (also called guanylic acid).
  • The enzyme PRPP glutamyl amidotransferase is controlled by feedback inhibition of nucleotides.
  • The rate limiting step of de novo Purine Synthesis is PRPP Glutamyl amidotransferase.

Salvage pathway-

  • Free purine bases (adenine, guanine and hypoxanthine) and purine nucleosides are formed in cells during the metabolic degradation of nucleic acids and nucleotides. These free purine           bases and purine nucleosides are reused in the formation of purine nucleotides. This is called salvage pathway

Catabolism of Purine Metabolism- (Degradation)

  • Adenine nucleotides catabolism- liver, heart muscle, Skeletal muscle, GIT mucosa
  • Guanine nucleotides catabolism- liver, spleen, kidney, pancreas, GIT mucosa.
  • Human catabolises purine to uric acid.
  • First metabolic product of purines is Xanthine.
  • In higher primates, Allantoin by enzyme uricase is the end product.

Disorders of Purine Metabolism-

  • Gout
  • Lesch- Nyhan Syndrome
  • Adenosine deaminase deficiency
  • Purine nucleoside phophorylase deficiency

Exam Important

  • First Nucleotide formed in Purine Synthesis-lnosine Mono Phosphate (lMP)
  • Liver is the major site of nucleotide biosynthesis.
  • Tissues which cannot synthesis purine nucleotides by de nevo pathway are- brain, erythrocytes and leuckocytes.
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