Question

Unlike the other 19 standard amino acids, lysine does not undergo transamination. What is the fate of its α- and ε-amino groups when it is catabolized?

Short answer

Both α- and ε-amino groups end up as glutamate.

Step-by-step solution

Definition of Transamination

Transamination, a chemical reaction that transfers an amino group to aketoacid to form new amino acids. This pathway is responsible for the deamination of most amino acids. This is one of the major degradation pathways which convertessential amino acids tonon-essential amino acids.

Degradation of lysine

lysineis degraded toacetoacetateand2CO₂. During thepathway,lysineloses its aminogroups through2separate reactions.

First amino group that is removed is ϵ-aminogroup in first2steps oflysinedegradation pathway.

Lysine forms saccharopine by reacting with α-ketoglutarate, which then releasesglutamatein step2.

ϵ-Amino group of lysine is removed as part of glutamate.Part of molecule that is removed as glutamate is coloured blue.

Pathway of lysine degradation

Products of the above reaction

α-Amino group is removed by transferring amino group to α-ketoglutarate, formingglutamate.

This reactionuses aminoadipate aminotransferase as an enzyme.

Conversion of α-Aminoadipate into α-Ketodipate

Both α- and ε-amino groups end up as glutamate.