Part of the bacABCDEF operon responsible for the biosynthesis of the nonribosomally synthesized dipeptide antibiotic bacilysin, composed of L-alanine and L-anticapsin. Bacilysin is an irreversible inactivator of the glutaminase domain of glucosamine synthetase. BacB catalyzes the allylic isomerization of the endocyclic-delta(4),delta(8)-7R-dihydro-hydroxyphenylpyruvate (en-H2HPP) to generate a mixture of 3E,7R- and 3Z, 7R-olefins of the exocyclic-delta(3),delta(5)-dihydro-hydroxyphenylpyruvate (ex-H2HPP). 3-[(4R)-4-hydroxycyclohexa-1,5-dien-1-yl]-2-oxopropanoate = 3-[(1E,4R)-4-hydroxycyclohex-2-en-1-ylidene]pyruvate Binds 2 Fe(2+) or Co(2+) ions per subunit. Antibiotic biosynthesis; bacilysin biosynthesis. Monomer.