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Concentration-dependent effects of disulfonic stilbenes on colonic chloride transport.

Stripped rabbit colonic mucosa was studied in vitro in Ussing chambers to determine effects of the disulfonic stilbenes 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonate (SITS) and 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS) and the diuretic furosemide on unidirectional and net Cl fluxes. Results from these studies reveal that SITS (1 mM) added to either the serosal or mucosal bathing solution reduced both unidirectional Cl fluxes with no significant change in net Cl flux. The effects of SITS do not appear to be mediated by an effect on the shunt permeability since SITS (1 mM) did not alter either the intercept or slope of the Na concentration dependence of the serosal-to-mucosal Na flux. Furosemide (1 mM) decreased the serosal-to-mucosal Cl flux without altering short-circuit current (Isc) when added to the luminal bathing solution and reduced both unidirectional fluxes and increased Isc when added to the serosal bathing solution. DIDS (0.5 mM) added to the luminal bathing solution did not alter unidirectional Cl fluxes or Isc. However, serosal addition of DIDS produced dose-dependent changes in Cl transport. At 5 microM DIDS reduced the mucosal-to-serosal Cl flux without altering the serosal-to-mucosal flux or Isc. At 50 microM DIDS reduced the mucosal-to-serosal Cl flux and increased Isc, and at 0.5 mM DIDS increased the serosal-to-mucosal Cl flux, reduced the mucosal-to-serosal Cl flux, and increased Isc and transepithelial conductance. The effect of 0.5 mM DIDS on Isc was reduced by Ca removal from the serosal bathing solution and by the loop diuretics furosemide and bumetanide.(ABSTRACT TRUNCATED AT 250 WORDS)

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

Structure-based inhibitor design for an enzyme that binds different steroids: a potent inhibitor for human type 5 17beta-hydroxysteroid dehydrogenase.

Human type 5 17beta-hydroxysteroid dehydrogenase plays a crucial role in local androgen formation in prostate tissue. Several chemicals were synthesized and tested for their ability to inhibit this enzyme, and a series of estradiol derivatives bearing a lactone on the D-ring were found to inhibit its activity efficiently. The crystal structure of the type 5 enzyme in complex with NADP and such a novel inhibitor, EM1404, was determined to a resolution of 1.30 A. Significantly more hydrogen bonding and hydrophobic interactions were defined between EM1404 and the enzyme than in the substrate ternary complex. The lactone ring of EM1404 accounts for important interactions with the enzyme, whereas the amide group at the opposite end of the inhibitor contributes to the stability of three protein loops involved in the construction of the substrate binding site. EM1404 has a strong competitive inhibition, with a Ki of 6.9+/-1.4 nM, demonstrating 40 times higher affinity than that of the best inhibitor previously reported. This is observed despite the fact that the inhibitor occupies only part of the binding cavity. Attempts to soak the inhibitor into crystals of the binary complex with NADP were unsuccessful, yielding a structure with a polyethylene glycol fragment occupying the substrate binding site. The relative crystal packing is discussed. Combined studies of small molecule inhibitor synthesis, x-ray crystallography, enzyme inhibition, and molecular modeling make it possible to analyze the plasticity of the substrate binding site of the enzyme, which is essential for developing more potent and specific inhibitors for hormone-dependent cancer therapy.

17-Hydroxysteroid Dehydrogenases↗