In which form of aminoacid is ammonia transported from skeletal muscle to liver?
Ans. is 'c' i.e., Alanine* Two mechanisms are available for transport of ammonia from the peripheral tissues to the liver.1) In the form of glutamine# In 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 route.# Glutamine is a nontoxic major transport form of ammonia. The glutamine is transported 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). The ammonia is converted by liver to urea.GlutamineH2O-----------------GlutaminaseGlutamate + NH4# 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 alanine# Alanine transports 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 transported to liver. In liver alanine is converted to pyruvate and glutamate by transamination reaction. Glutamate undergoes oxidative deamination to release free ammonia, which is converted to urea. Pyruvate is converted to glucose by gluconeogenesis.
Glutamate
Glutamine
Alanine
Glycine
Proteins and Amino Acids