Question

Name the enzymes (above and below the arrow) that complete the following conversions a) alpha- ketoglutarate to glutamate b) glutamate to alpha-ketoglutarate c) glutamate to glutamine d) glutamine to glutamate. Describe which if any are regulated. Why do you think this series of reactions is important?

Alpha-ketoglutarate  glutamate  glutamine

Answer 1

a,b. Glutamate dehydrogenase (GDH) is a hexameric enzyme that catalyzes the reversible conversion of glutamate to α-ketoglutarate and ammonia while reducing NAD(P)⁺ to NAD(P)H. It is found in all living organisms serving both catabolic and anabolic reactions.

Glutamate + NADP+ α-ketoglutarate + ammonia

c. Glutamine synthetase is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine:

Glutamate + ATP + NH₃ → Glutamine + ADP + phosphate

Glutamine synthetase activity in E. coli is subject to inhibition by seven different end products of glutamine metabolism, namely, by tryptophan, histidine, carbamyl-phosphate, CTP, AMP, glucose-6-phosphate, and NAD+, and also by serine, alanine, and glycine.

d. Glutaminase catalyzes the following reaction: Glutamine + H₂O → glutamate + NH₃.