Question

Summarize the reactions that release an amino acid’s amino group as ammonia.

Short answer

In the reaction of glutamate dehydrogenase (GDH) releases ammonia.

Step-by-step solution

Glutamate dehydrogenase.  

Naturally, transamination does not lead to any net deamination. However, glutamate dehydrogenase (GDH) has the ability to oxidatively deaminate glutamate, creating ammonia and regenerating -ketoglutarate for further transamination processes.

Formation of α-iminoglutarate

The only known enzyme that can take either NAD+ or NADP+ as its redox cofactor is glutamate dehydrogenase, a mitochondrial enzyme. In order to create -iminoglutarate, which is then hydrolyzed into -ketoglutarate and ammonium ion, oxidation is considered to take place when a hydride ion is transferred from glutamate's C atom to NAD(P)+.