Function
Catalyzes both 1,3- and 1,5-keto-enol tautomerization of the diacid 2-hydroxymuconate (2-hydroxy-2,4-hexadienedioate) to produce 2-oxo-4-hexenedioate. This reaction is highly stereoselective and produces a mixture of stereoisomers, where the (3S)-isomer of 2-oxo-4-hexenedioate predominates. Also catalyzes the tautomerization of 2-hydroxymuconate to 2-oxo-3-hexenedioate, however this reaction is slower and occurs after the tautomerization of 2-hydroxymuconate to 2-oxo-4-hexenedioate. Using 2-hydroxy-2,4-pentadienoate, phenylenolpyruvate, (p-hydroxyphenyl)-enolpyruvate and 2-hydroxy-2,4-heptadiene-1,7-dioate, YwhB is a highly efficient 1,3-keto-enol tautomerase, but clearly not a 1,5-keto-enol tautomerase. Tautomerization of the two monoacids 2-hydroxy-2,4-pentadienoate and phenylenolpyruvate produces a mixture of stereoisomers, where the (3R)-isomers predominate.