Identification of L-methionine-S-sulfoximine as the convulsant isomer of methionine sulfoximine.

The convulsant agent methionine sulfoximine inhibits brain glutamine synthetase irreversibly and the inhibitor becomes bound to the active site of the enzyme as methionine sulfoximine phosphate. Only one of the four isomers of methionine sulfoximine, L-methionine-S-sulfoximine, inhibits glutamine synthetase. In the present work, D-methionine-SR-sulfoximine, and highly purified preparations of L-methionine-S-sulfoximine and L-methionine-R-sulfoximine were tested in mice for convulsant activity; only L-methionine-S-sulfoximine produced convulsions. The finding that only one of the four optical isomers of methionine sulfoximine induces convulsions, and that only this same isomer inhibits glutamine synthetase, lends support to the conclusion that these two effects of methionine sulfoximine are closely connected.