xaa represented methionine s , s-dioxide , methionine s-oxide , methionine sulfoximine , and 2-amino-4-phosphonobutyric acid , i.e . transition state analogs of glutamine synthetase and gamma-glutamyl-cysteine synthetase , which catalyze the same type of reaction as our target enzyme .
C0025646
methionine
C0025649
methionine sulfoximine