Methionine sulfoximine (MSO, also known as MetSox[1]) is an irreversible glutamine synthetase inhibitor.

These affect the longevity of the model mouse for Lou Gehrig's disease.

[3] Overproduction of glutamate results to excitotoxicity, which kills the cell.

Since methionine sulfoximine inhibits glutamate production in the brain, it prevents excitotoxicity.

The resulting product acts as a transition state analog that is unable to diffuse from the active site, thereby inhibiting the enzyme.