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EC 1.17.99.5 Details
EC number
1.17.99.5
Accepted name
bile-acid 7α-dehydroxylase
Reaction
(1) deoxycholate + FAD + H2O = cholate + FADH2;;(2) lithocholate + FAD + H2O = chenodeoxycholate + FADH2
Other name(s)
cholate 7α-dehydroxylase, 7α-dehydroxylase, bile acid 7-dehydroxylase, deoxycholate:NAD+ oxidoreductase
Systematic name
deoxycholate:FAD oxidoreductase (7α-dehydroxylating)
CAS registry number
85130-33-2
Comment
Under physiological conditions, the reactions occur in the reverse direction to that shown above. This enzyme is highly specific for bile-acid substrates and requires a free C-24 carboxy group and an unhindered 7α-hydroxy group on the B-ring of the steroid nucleus for activity, as found in cholate and chenodeoxycholate. The reaction is stimulated by the presence of NAD+ but is inhibited by excess NADH. This unusual regulation by the NAD+/NADH ratio is most likely the result of the intermediates being linked at C-24 by an anhydride bond to the 5′-diphosphate of 3′-phospho-ADP [2,5,6]. Allo-deoxycholate is also formed as a side-product of the 7α-dehydroxylation of cholate [6]. The enzyme is present in intestinal anaerobic bacteria [6], even though its products are important in mammalian physiology.
History
created 2005 as EC 1.17.1.6, transferred 2006 to EC 1.17.99.5, deleted 2014
EC Tree
1.1.99.15 created 1978, deleted 1980
1.1.99.17 created 1982, deleted 2003