Which amino acid binds NH4+ covalently and makes it non-toxic for transpoation ?

Ans. is 'c' i.e., Glutamate DISPOSAL/DETOXIFICATION OF AMMONIA1. First line of Defense (Trapping of ammonia)Being highly toxic, ammonia should be eliminated or detoxified, as and when it is formed. Even very minute quantity of ammonia may produce toxicity in central nervous system.But, ammonia is always produced by almost all cells, including neurons.The intracellular ammonia is immediately trapped by glutamic acid to form glutamine, especially in brain cells .The glutamine is then transpoed to liver, where the reaction is reversed by the enzyme glutaminase .The ammonia thus generated is immediately detoxified into urea.Aspaic acid may also undergo similar reaction to form asparagine .2. Transpoation of AmmoniaInside the cells of almost all tissues, the transamination of amino acids produce glutamic acid.However, glutamate dehydrogenase is available only in the liver.Therefore, the final deamination and production of ammonia is taking place in the liver .Thus, glutamic acid acts as the link between amino groups of amino acids and ammonia.The concentration of glutamic acid in blood is 10 times more than other amino acids.Glutamine is the transpo forms of ammonia from brain and intestine to liver; while alanine is the transpo form from muscle.3. Final disposalThe ammonia from all over the body thus reaches liver. It is then detoxified to urea by liver cells, and then excreted through kidneys.Urea is the end product of protein metabolism.