 YUCCA flavin monooxygenase

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.^[ref]

Let IPyA and IAA denote the two anionic organic participants in that reaction. The net balance isThe 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.^[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.^[ref]