Figure 2.

Two proposed metabolic pathways for the amino acid Tryptophan (Trp).

Trp is oxidized into indole-3-acetaloxime (IAOx) by the Cytochrome P450 CYP79B2/B3. IAOx is a substrate for another P450, CYP83B1, which is also called SUPERROOT2 (SUR2). SUR2 converts IAOx into 1-aci-nitro-2 indolyl-ethane, which is further converted to Indol-3-ylmethyl S-alkyl-thiohydroximate by an unknown mechanism. SUPERROOT1 (SUR1) is a C-S lyase that converts S-alkyl-thiohydroximate to thiohydroximate. Both SUR1 and SUR2 are important for glucosinolate biosynthesis. Inactivation either SUR1 or SUR2 leads to the accumulation of IAOx, which is converted into IAA by an unknown mechanism. Trp can also be oxidized to indole-3-acetamide (IAM) by the bacterial auxin biosynthesis enzyme iaaM Trp-2-monooxygenase. IAM is hydrolyzed into IAA by the bacterial enzyme iaaH. Overexpression of iaaM or CYP79B2 leads to auxin overproduction phenotypes. Question mark indicates that enzymes for the steps are not known.