The conversion of the amino acid glutamine to α-ketoglutarate takes place in two reaction steps:
1. Hydrolysis of the amino group of glutamine yielding glutamate and ammonium.
Catalyzing enzyme: glutaminase (EC 3.5.1.2)
2. Glutamate can be excreted or can be further metabolized to α-ketoglutarate.
For the conversion of glutamate to α-ketoglutarate three different reactions are possible:
Catalyzing enzymes: 
*glutamate dehydrogenase (GlDH), EC 1.4.1.2
*glutamate pyruvate transaminase (GPT), also called alanine transaminase (ALT), EC 2.6.1.2
*glutamate oxaloacetate transaminase (GOT), also called aspartate transaminase (AST), EC 2.6.1.1 (component of the malate aspartate shuttle)