Biosynthesis of Amino Acids: 3 Ways

Biosynthesis of amino acids. The ways are: 1. Ammonium Assimilation 2. Transamination and 3. Other Methods.

Way # 1. Ammonium Assimilation:

(A) Reductive Ammination:

Inorganic nitrogen in the form of NH₃ or ammonium (NH₄⁺) produced as a result of reduction of nitrates or biological nitrogen fixation or obtained from the soil, react with a-ketoglutaric acid (an intermediate of Krebs’ Cycle) in the presence of the enzyme glutamic dehydrognase (GDH) and reduced coenzyme NADPH + H to form an amino acid, the glutamic acid (i.e., glutamate) and thus is converted into organic form.

(B) GS/GOGAT – Pathway:

Inorganic nitrogen in the form of ammonium can also be converted into amino acid (i.e., organic form) by sequential actions of two enzymes, glutamine synthetase (GS) and glutamate synthase (also known as glutamine: 2-oxo-glutarate aminotransferase or GOGAT) found in plants.

Way # 2. Transamination:

The various other amino acids which ultimately condense to form proteins are produced by transamination reactions involving the transfer of amino group from glutamic acid to the keto position of the corresponding keto acid.

Amino group from other amino acids except glutamic acid may also be transferred to other keto acids forming corresponding amino acids. Transamination reactions take place in the presence of enzymes transminases (aminotransferases) which require coenzyme pyridoxal phosphate (a derivative of vitamin B₆ i.e., pyridoxine).

The coenzyme pyridoxal phosphate acts as carrier of amino group. It picks up the amino group from the donor amino acid and is converted into pyridoxamine phosphate. The latter transfers this amino group to the acceptor keto acid forming a new amino acid and itself is converted into pyridoxal phosphate as shown in the figure 9.6.

Although a large number of transamination reactions are now known but the following 3 are very common:

Way # 3. Other Methods:

Amino acids may also be produced by the transformation of acid amides and other nitrogenous compounds or by the hydrolysis of proteins by proteolytic enzymes.