Functions in the bile acid 7alpha-dehydroxylation pathway, which forms secondary bile acids via the 7alpha-dehydroxylation of primary bile acids, and is carried out by intestinal anaerobic bacteria. Catalyzes the dehydration step in this pathway, yielding a 3-oxo-Delta(4,6)-bile acid-CoA intermediate. In vitro, can act on the free bile acids (non CoA-conjugated) 7-alpha,12-alpha-dihydroxy-3-oxochol-4-enoate and 7-alpha-hydroxy-3-oxochol-4-enoate, but not on 7-alpha,12-alpha-dihydroxy-3-oxo-5-beta-cholanate, 3-alpha,7-alpha,12-alpha-trihydroxy-5-beta-cholanate or 7-beta-hydroxy-3-oxochol-4-enoate. 7alpha,12alpha-dihydroxy-3-oxochol-4-en-24-oyl-CoA = 12alpha-hydroxy-3-oxochola-4,6-dien-24-oyl-CoA + H2O 7alpha-hydroxy-3-oxochol-4-en-24-oyl-CoA = 3-oxochol-4,6-dien-24-oyl-CoA + H2O 7alpha,12alpha-dihydroxy-3-oxochol-4-en-24-oate = 12alpha-hydroxy-3-oxochola-4,6-dien-24-oate + H2O 7alpha-hydroxy-3-oxochol-4-en-24-oate = 3-oxochola-4,6-dien-24-oate + H2O Lipid metabolism; bile acid biosynthesis. Homodimer. Induced by bile acids such as cholate.