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. BacA is an unusual prephenate decarboxylase that avoids the typical aromatization of the cyclohexadienol ring of prephenate. BacA catalyzes the protonation of prephenate (1-carboxy-4-hydroxy-alpha-oxo-2,5-cyclohexadiene-1-propanoic acid) at C6 position, followed by a decarboxylation to produce the endocyclic-delta(4),delta(8)-7R-dihydro-hydroxyphenylpyruvate (en-H2HPP). En-H2HPP is able to undergo a slow nonenzymatic isomerization to produce the exocyclic-delta(3),delta(5)-dihydro-hydroxyphenylpyruvate (ex-H2HPP). BacA isomerizes only the pro-R double bond in prephenate. H(+) + prephenate = 3-[(4R)-4-hydroxycyclohexa-1,5-dien-1-yl]-2-oxopropanoate + CO2 Antibiotic biosynthesis; bacilysin biosynthesis. Belongs to the prephenate decarboxylase family.