In liver ammonia is formed from which amino acid ?
Ans. is 'b' i.e., Glutamine Transpo of ammoniaAmmonia is produced in most of the tissues. However, it should be transpoed to liver as urea cycle (formation of urea) occurs only in liver. Since free ammonia is highly toxic, it is never transpoed in free form in blood.Two mechanisms are available for transpo of ammonia from the peripheral tissues to the liver :1) In the form of glutamineIn many tissues like liver, kidney and brain, ammonia combines with glutamate to yield glutamine, by the action of glutamine synthase. The brain is a rich source of glutamine synthase and it predominantly detoxifies ammonia by this routeGlutamine is a nontoxic major transpo form of ammonia. The glutamine is transpoed by blood to liver where deamination (removal of amino group) of glutamine takes place. Glutaminase cleaves glutamine to yield glutamate and free ammonia ammonium ion). "[he ammonia is conveed by liver to urea.Formation and secretion ammonia by renal tubular cells maintain acid base balance. Ammonia is formed from glutamine by glutaminase. Excretion of ammonia increases in metabolic acidosis and decreases in metabolic alkalosis. 2) In the form of alanineAlanine transpos ammonia from muscles to liver through glucose-alanine cycle'.In muscle, glutamate is formed from ammonia and a-ketoglutarate by reversal of the glutamate dehydrogenase reaction. L-glutamate then transfers its a-amino group to pyruvate by transmination reaction to form alanine.Alanine is transpoed to liver. In liver alanine is conveed to pyruvate and glutamate by transamination reaction. Glutamate undergoes oxidative deamination to release free ammonia, which is conveed to urea.
Glycine
Glutamine
Isoleucine
Proline