Question

The bacterium Methylophilus methylotrophus can use methanol and ammonia for protein synthesis. The glutamate dehydrogenase gene from E. coli was introduced into M. methylotrophus using recombinant DNA techniques. Under high ammonia conditions, the introduction of the glutamate dehydrogenase gene into M. methylotrophus resulted in an increase in protein yield. Select the statements that are reasonable explanations for the increased protein yield in the modified M. methylotrophus. Glutamate dehydrogenase catalyzes the formation of glutamate and glutamine in a two-step process. Both glutamate and glutamine play a key role in amino acid synthesis, thus an increase in levels of glutamate and glutamine increase protein synthesis. Glutamate dehydrogenase has a low affinity for NH^+_4, and can only catalyze the formation of glutamate from alpha-ketoglutarate and NH^+_4, when the concentration of NH^+_4 is high. Glutamate dehydrogenase has a high affinity for NH^+_4, thus the rate of glutamate synthesis increases exponentially under high ammonia conditions. Glutamate is the amino group donor for most transamination reactions involving amino acids, thus an increase in glutamate concentration increases protein synthesis.

Answer 1

- Glutamate dehydrogenase has a low affinity for NH+4, and can only catalyze the formation of glutamate from alpha-ketoglutarate and NH+4, when the concentration of NH+4 is high.

- Glutamate is the amino group donor for most transamination reactions involving amino acids, thus an increase in glutamate concentration increases protein synthesis.

Step-by-step explanation:

Glutamate dehydrogenase (GLDH) is an enzyme found in prokaryotic and eukaryotic cells, which is known to catalyze the reversible oxidative deamination of glutamate (Glu) to alpha-ketoglutarate and ammonia at the same time the oxidation of NADH to NAD. In bacteria, this enzyme (GLDH) is efficient only at high concentrations of the ammonium cation (NH4+), because it has a low affinity for NH4+. Moreover, transamination is a pathway that involves the transfer of an amino group from one amino acid to a ketoacid in order to form new amino acids (this reaction is responsible for the deamination of most amino acids). Glu is the donor of amino groups in most of the reactions catalyzed by enzymes involved in the transamination between an amino acid and an alpha-keto acid. In consequence, in presence of GLDH, a high concentration of Glu will increase the production of new amino acids and therefore also protein synthesis.