Question

E. coli can convert glutamate to ornithine. Describe the two reactions that do so

Short answer

The two reactions involving the conversion of glutamate to ornithine are:

• Reduction of the carboxyl group
• Transamination reaction.

Step-by-step solution

Conversion of glutamate to ornithine

In E. coli, glutamate is converted to ornithine as a precursor to arginine. It occurs in two steps:

• Reduction of the carboxyl group
• Transamination

Reduction of the carboxyl group

In the reduction reaction, the $\gamma$ carbonyl group of glutamate is reduced to an aldehyde group. This reaction is coupled with a phosphorylation reaction, as the reduction reaction is endergonic and hence coupling with exergonic phosphorylation is necessary. The phosphorylation is catalyzed by an enzyme$\mathit{\gamma }\mathit{g}\mathit{l}\mathit{u}\mathit{t}\mathit{a}\mathit{m}\mathit{y}\mathit{l}\mathit{k}\mathit{i}\mathit{n}\mathit{a}\mathit{s}\mathit{e}$ with the usage of 1 $ATP$.The phosphorylated product is converted to glutamate-5-semialdehyde due to its instability.

Transamination reaction

Transamination reaction is the process in which the amino group from the molecule is removed and transferred to another molecule leaving behind a keto acid.The glutamate-5-semialdehyde is transaminated to ornithine and is catalyzed by an enzyme called ornithine- $\delta$-aminotransferase. The glutamate is used in the reaction to provide amino groups. It will be released as $\text{α-ketoglutarate}$ (keto acid).

Reactions of conversion of glutamate to ornithine