The enzyme from the bacterium Azospirillum brasilense also acts on some other substrates, including (indol-3-yl)pyruvate, with much lower efficiency. However, it only possesses classical Michaelis-Menten kinetics with phenylpyruvate. Aliphatic 2-oxo acids longer that 2-oxohexanoate are not substrates. cf. EC 4.1.1.74, indolepyruvate decarboxylase.