Extended Data Fig. 2: Independent testing of Trp AT activity, in reverse direction, for Arabidopsis AT enzymes.

The average Trp AT activity (right panel), in % conversion of indole-3-pyruvate (IPA) to Trp using one of seven amino donors tested (Fig. 2a), was compared with the Trp AT activity assays in the reverse direction (left panel, Trp to IPA conversion) using an independent method. Thirty-three AT enzymes were individually incubated with the Trp substrate (5 mM) and the mixture of three keto acid substrates, α-ketoglutarate, pyruvate, 4MTOB (1 mM each) for one hour, and the production of IPA was monitored after the reaction with the Salkowski reagent, which provides a distinct absorption at 530 nm. Data are means ± s.e.m. (n = 3 independent reactions). Individual data points are shown. Background values detected from the reactions with empty vector control were subtracted. A red arrow denotes the lack of Trp AT activity in TAA1 in the AT mapping data due to the substrate inhibition by IPA (Sato et al., 2022).