= YUCCA flavin monooxygenase
{c}
A <YUCCA flavin monooxygenase> is a member of a plant enzyme family involved in <auxin> biosynthesis. Its indole-3-pyruvate monooxygenase activity converts <indole-3-pyruvate> to <indole-3-acetate>, the conjugate base of <indole-3-acetic acid>, with loss of <carbon dioxide>. The official reaction is EC 1.14.13.168.<Enzyme Nomenclature by the IUBMB>[EC 1.14.13.168, Reaction, Systematic name and Comments]{ref}
Let IPyA and IAA denote the two anionic organic participants in that reaction. The net balance is
$$
\mathrm{IPyA+NADPH+H^++O_2\longrightarrow IAA+NADP^++H_2O+CO_2}.
$$
The reaction uses <NADPH> and <oxygen>. Together with an upstream <transamination> step, it connects <tryptophan> to <indole-3-acetic acid>. The net transformation removes one carbon from the substrate's side chain; it does not merely change the substrate's concentration without changing its chemical identity.<Enzyme Nomenclature by the IUBMB>[EC 1.14.13.168, Reaction and Comments]{ref}
In a constructed ideal inventory, 40 nanomoles of <indole-3-pyruvate>, 20 of <NADPH> and 30 of <oxygen> permit at most 20 nanomoles each of <indole-3-acetate> and <carbon dioxide> through the stated reaction. That ceiling assumes no replenishment or side reactions; donor oxidation alone would not identify the organic product.
A developmental experiment supplies a different kind of evidence. In the parasitic plant <Phtheirospermum japonicum>, local YUC3 expression and altered gene expression were associated with changes in haustorium development. Such observations connect local <auxin> production to organ development, while a biochemical assay asks which reaction the enzyme performs.<Local Auxin Biosynthesis Mediated by a YUCCA Flavin Monooxygenase Regulates Haustorium Development in the Parasitic Plant Phtheirospermum japonicum by Juliane K. Ishida and others>[Abstract, YUC3 localization, knockdown and ectopic-expression experiments]{ref}
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