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Indole-3-pyruvate is the indole-substituted pyruvate anion named systematically 3-(1H-indol-3-yl)-2-oxopropanoate. It is the conjugate base of indole-3-pyruvic acid. The three-carbon side chain distinguishes it from indole-3-acetate, whose corresponding side chain has two carbons.^[ref]

A biological example is the plant route from tryptophan to the auxin indole-3-acetate. A transamination supplies indole-3-pyruvate; a YUCCA flavin monooxygenase then participates in its conversion to indole-3-acetate. The accepted net reaction uses NADPH and molecular oxygen and releases carbon dioxide, so the step is not simply a change in protonation.^[ref]

An original carbon inventory makes the one-carbon loss clear. The indole framework contributes eight carbon atoms, giving eleven in indole-3-pyruvate and ten in indole-3-acetate. Converting 20 nmol of substrate according to the stated reaction distributes $20(11)=220$ nmol of carbon atoms between $20(10)=200$ nmol in the organic product and 20 nmol in carbon dioxide. The balance checks the net stoichiometry, without establishing the provenance of individual oxygen atoms or a reaction rate.