Bithionol
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| Synonyms | 2,4-dichloro- 6-(3,5-dichloro- 2-hydroxyphenyl)sulfanylphenol |
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| ECHA InfoCard | 100.002.333 |
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| Formula | C12H6Cl4O2S |
| Molar mass | 356.05 g/mol |
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Bithionol is an anthelmintic used to treat Anoplocephala perfoliata (tapeworms) in horses and Fasciola hepatica (liver flukes).
Bithionol has antibacterial and anthelmintic properties along with algaecide activity. It was formerly used in soaps and cosmetics until the FDA banned it for its photosensitizing effects. The compound has been known to cause photocontact sensitization.
Bithionol has been shown to be a potent inhibitor of soluble adenylyl cyclase (sAC), an intracellular enzyme important in the catalysis of ATP to cAMP. Soluble adenylyl cyclase is uniquely activated by bicarbonate. The cAMP formed by this enzyme is associated with capacitation of sperm, eye pressure regulation, acid-base regulation, and astrocyte/neuron communication.
Based on its relationship to the organochlorine, hexachlorophene, which has been shown to be a successful, but isomer-specific inhibitor of soluble adenylyl cyclase, bithionol was chosen to study potential inhibitors of the sAC enzyme. These two organochlorine compounds have similar chemical structures. Bithionol has two aromatic rings with a sulfur atom bonded between them and multiple chlorine ions and hydroxyl groups coming off of the phenyl groups. These functional groups are capable of hydrophobic, ionic, and polar interactions.
These intermolecular interactions are capable of binding bithionol to the bicarbonate binding site of soluble adenylyl cyclase efficiently enough to cause a sort of competitive inhibition with the usual bicarbonate substrate. The side chain of Arginine 176 within the bicarbonate binding site of the sAC protein interacts significantly with the aromatic ring of the bithionol molecule. This allosteric, conformational change interferes with the ability of the active site of sAC to adequately bind ATP to convert it into cAMP. The Arginine 176 usually interacts with the ATP and other catalytic ions at the active site, so when it turns from its normal position to interact with the bithionol inhibitor, it no longer functions in keeping the ATP bound to the active site.
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