Question

Amino acid that carries ammonia from skeletal muscle to liver is

• A. Alanine
• B. Arginine
• C. Methionine
• D. Glutamate

Answer 1

Answer: (A)

Alanine

There are two mechanisms in humans which help in the transport of ammonia to liver from tissues so that ammonia can be converted into urea. In most of the tissues ammonia is combined with glutamate in the presence of enzyme glutamate synthetase which is then transported in blood to the liver. In the liver glutamine is broken down to release ammonia and glutamate by enzyme glutaminase. In the second type of mechanism which takes place primarily in muscles, the pyruvate formed in glycolysis is transaminated to form alanine. This alanine is then transported to liver where it is again converted to pyruvate. In liver pyruvate is used to synthesize glucose by gluconeogenesis which enters the blood and can be utilized by muscles. This pathway is known as glucose-alanine cycle. Arginine is a semi essential basic amino acid which takes part in urea cycle in liver. Methionine is a sulphur containing essential amino acid. Thus, the correct answer is option A.