Describe two ways by which NH4+ is used to synthesize amino acids in plants.
NH4+ (ammonium ion) can undergo two types of reactions to produce amino acids:
Transamination − transfer of the amino group from one amino acid to the keto group of the keto acid catalysed by the enzyme transaminase
E.g., formation of amides, asparagine and glutamine from amino acids, aspartic acid and glutamic acid, by the addition of the amino group
Fixed nitrogen, as in soyabean, is sometimes transported as ureides along with transpiration.
Reductive amination − glutamate is formed from NH4+ by the reaction with α-ketoglutaric acid.
α -ketoglutaric acid + NH4+ + NADPH
Glutamate + H2O + NADP