Catalyzes the dehydration of chorismate into 3-[(1-carboxyvinyl)oxy]benzoate, a step in the biosynthesis of menaquinone (MK, vitamin K2). chorismate = 3-[(1-carboxyvinyl)-oxy]benzoate + H2O Quinol/quinone metabolism; menaquinone biosynthesis. Cells lacking this gene do not grow on standard rich medium; however, growth of these mutants is readily rescued by the addition of aminodeoxyfutalosine, but not futalosine. Belongs to the MqnA/MqnD family. MqnA subfamily.