Aminotransferases in Higher Plants

This chapter discusses aminotransferases in higher plants. The aminotransferases or transaminases are enzymes catalyzing the transfer of an amino group, plus a proton and an electron pair, from an amino donor compound to the carbonyl position of an amino acceptor compound. This process is known as transamination. Usually, an amino acid acts as the amino donor and a 2-keto acid as the amino acceptor. The result is the formation of a new amino acid plus the keto acid analogue of the amino acid, which originally serves as the amino donor. In some cases, aldehydes can serve as amino acceptor substrates and amines can act as donors. Most transaminations are freely reversible processes. The best characterized plant aminotransferase is glutamate-oxaloacetate transaminase, which catalyzes the reversible interconversions between glutamate and aspartate, and their 2-keto analogues. The enzymatic transfer of amino groups plays an important part in many metabolic processes, where the interconversion of nitrogen-containing molecules is involved. Nitrogen, following its initial assimilation into glutamine and glutamate, can be distributed to many other compounds by the action of aminotransferases.