Purines, Pyrimidines and Nucleic Acid Metabolism
Regarding NH3 in glutamine-true is
|A||Cannot be used for purine synthesis|
|B||Cannot be degraded by enzymes|
|D||Major excretory pathway is kidney|
The sources of the nitrogen and carbon atoms of the purine ring (Adenine + Guanine): Glycine provides C-4, C-5 and N-7 of the purine ring.
Amide nitrogen of glutamine provides N-3 and N-9 of purine ring
Fig.: The source of the nitrogen and carbon atoms of the purine ring. Atoms 4, 5 and 7 (shaded) derive from Glycine
a. During purine synthesis, in second step, Amide nitrogen of glutamine (not amino gp of nitrogen), displace pyrophosphate from 5-phosphoribosyl-1-pyrophosphate (PRPP) to form 5- phospho-β-d-ribosylamine (III).
b. While ammonia is constantly produced in the tissue it is rapidly removed from the circulation by the liver and converted to glutamate, glutamine and ultimately to urea.
c. In brain tissue, the major mechanism for detoxification of NH3 (Ammonia) is glutamine formation.