= Indole-3-pyruvic acid
\b[Indole-3-pyruvic acid] is an <indole>-substituted oxo <carboxylic acid>, systematically 3-(1H-indol-3-yl)-2-oxopropanoic acid. Its neutral <molecular formula> is $\mathrm{C_{11}H_9NO_3}$. Its <conjugate base> is <indole-3-pyruvate>, which retains the same carbon skeleton after loss of a proton.<Indole-3-pyruvic acid in PubChem>[CID803, Names and Identifiers, Molecular Formula and structure; anion CID5460337.]{ref}
The acid/base relationship can be represented as
$$
\mathrm{C_{11}H_9NO_3}\rightleftharpoons\mathrm{H^+}+\mathrm{C_{11}H_8NO_3^-}.
$$
Both sides have eleven carbon atoms and three oxygen atoms; the change concerns protonation and charge. This is different from the biochemical conversion of <indole-3-pyruvate> to <indole-3-acetate>, which releases <carbon dioxide> and changes the carbon inventory of the organic product.<Enzyme Nomenclature by the IUBMB>[EC1.14.13.168, substrate/product Glossary and accepted net reaction.]{ref}
An illuminating comparison is therefore between changing a solution's acid/base conditions and changing a metabolite's carbon skeleton. Those operations can alter names or measured signals for different reasons. Identifying the <chemical structure> and protonation state prevents the acid, its anion and the shorter-side-chain <auxin> product from being treated as one interchangeable chemical identity.
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