Identification of S-1-propenyl-L-cysteine as the catalytic product of AfGGT1 and a key intermediate in isoalliin biosynthesis in Allium fistulosum. L

Our findings reveal that pyruvic acid content is generally higher in <i>Allium fistulosum</i> than in <i>A. cepa</i>. In <i>A. fistulosum</i>, the bulbs contain more pyruvic acid than the leaves, while in <i>A. cepa</i>, the inner bulb layers exhibit higher levels compared to the outer layers. We demonstrate that <i>A. fistulosum</i> γ-glutamyl transpeptidase 1 (AfGGT1) catalyzes the production of S-1-propenyl-L-cysteine from γ-glutamyl-S-1-propenylcysteine, whereas AfGGT2 and AfGGT3 lack catalytic activity. In natural populations of <i>A. fistulosum</i>, AfGGT1 expression shows a strong positive correlation with pyruvic acid content (R² = 0.6976). The optimal catalytic conditions for AfGGT1 are pH 7 and 37 °C, with a K_m value of 0.2686 mM under these conditions. Molecular docking studies further reveal distinct substrate-binding conformations among AfGGT1, AfGGT2, and AfGGT3, highlighting functional divergence within the enzyme family.