In the process of obtaining nitrogen for making proteins, plants get nitrogen either as nitrates or ammonia. Ammonium form is highly toxic for the plant and hence, it is directly used in the amino acid production in two steps.

First one is called the reactive amination, where the ammonia reacts with $\alpha$ -ketoglutaric acid to form glutamate. This reaction is catalyzed by the enzyme glutamate dehydrogenase. Next part is the transamination where the amino group of amino acid is transferred to keto group of keto acid. Transaminase catalyses this process.