The role of cytoplasmic proteins in hepatic bile acid transport.
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3-Hydroxysteroid Dehydrogenases↗
Biomedical subjects
A Stolz
Publications and source records attributed to A Stolz.
Subunit heterogeneity of cationic human hepatic glutathione S-transferases.
We have purified the major reduced glutathione (GSH) S-transferases from 3 apparently normal human livers: two obtained at surgery and one at autopsy. Purification was by sequential gel filtration. GSH-affinity chromatography, and chromatofocusing. All three livers exhibited the same two major transferase peaks from chromatofocusing at pH 9.0 and 8.7 (designated C1 and C2, respectively) and several (2-4) minor peaks. Another major form (designated A1) from two livers eluted from chromatofocusing at pH 5.4, whereas the major form from the third liver (designated N1) eluted near neutral (pH 6.8). The transferase from erythrocytes eluted at pH 4.6. Isoelectric focusing revealed that the true pI of A1 was pH 7.1 indicating that C1, C2 and A1 are all cationic. In sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, C1, C2 and A1 exhibited the same single subunit (25,000) whereas N1 was different (26,000). The erythrocyte enzyme had a smaller subunit (23,500). Urea/SDS-polyacrylamide gel electrophoresis resolved the apparent single subunit of A1, C1 and C2 into two distinct subunits. C1 from all 3 livers was a homodimer of the faster migrating subunit (designated subunit I); C2 was a heterodimer (designated I-II); and A1 was a homodimer of the slower migrating subunit (designated subunit II). Hybridization experiments demonstrated that by mixing C1 and A1 we could produce C2 whereas dissociation and reassociation of the subunits of C2 generated C1 and A1 as well as C2. Rabbit antiserum to C1 recognized C1 and C2, but not A1. Thus, the cationic human hepatic transferases are dimers of two distinct subunits.
Amino Acids↗
3 alpha-hydroxysteroid dehydrogenase activity of the Y' bile acid binders in rat liver cytosol. Identification, kinetics, and physiologic significance.
Rat Y' bile acid binders (33 kD) have been previously recognized as cytosolic bile acid binding proteins (Sugiyama, Y., T. Yamada, and N. Kaplowitz, 1983, J. Biol. Chem., 258:3602-3607). We have now determined that these Y' binders are 3 alpha-hydroxysteroid dehydrogenases (3 alpha-HSD), bile acid-metabolizing enzymes. 3 alpha-HSD activity copurified with lithocholic acid-binding activity after sequential gel filtration, chromatofocusing, and affinity chromatography. Three peaks of 3 alpha-HSD activity (I, II, III) were observed in chromatofocusing and all were identified on Western blot by a specific Y' binder antiserum. 3 alpha-HSD-I, the predominant form, was purified and functioned best as a reductase at pH 7.0 with a marked preference for NADPH. Michaelis constant values for mono- and dihydroxy bile acids were 1-2 microM, and cholic acid competitively inhibited the reduction of 3-oxo-cholic acid. Under normal redox conditions, partially purified 3 alpha-HSD-I and freshly isolated hepatocytes catalyzed the rapid reduction of 3-oxo-cholic to cholic acid without formation of isocholic acid, whereas the reverse reaction was negligible. The Y' bile acid binders are therefore 3 alpha-HSD, which preferentially and stereospecifically catalyze the reduction of 3-oxo-bile acids to 3 alpha-hydroxy bile acids.
3-Hydroxysteroid Dehydrogenases↗
Cyclical oxidation-reduction of the C3 position on bile acids catalyzed by rat hepatic 3 alpha-hydroxysteroid dehydrogenase. I. Studies with the purified enzyme, isolated rat hepatocytes, and inhibition by indomethacin.
We recently identified that the Y' bile acid binders are 3 alpha-hydroxysteroid dehydrogenases (3 alpha-HSD). In the present studies, purified 3 alpha-HSD catalyzed rapid 3H loss from [3 beta-3H, C24-14C]lithocholic and chenodeoxycholic acids without net conversion to 3-oxo bile acids under physiologic pH and redox conditions. [3 beta-3H]Cholic acid was a poor substrate. The Y' fraction of hepatic cytosol was exclusively responsible for this activity and 3H was transferred selectively to NADP+. Time-dependent 3H loss was also seen in isolated hepatocytes. Further hydroxylation products of lithocholic and chenodeoxycholic acids lost 3H at the same rate, whereas 3H loss from lithocholic acid rapidly ceased, which suggests compartmentation of this bile acid in hepatocytes. Indomethacin inhibited 3H loss from bile acids either in incubations with the pure enzyme or in isolated hepatocytes. Indomethacin did not alter the initial uptake rate of bile acids by hepatocytes, but caused a redistribution of unconjugated bile acids into the medium at early time points (2.5 and 5.0 min) and that of conjugated bile acids at later time intervals (30 min). 3H loss from the 3 beta position therefore can be used to probe the interaction between bile acids and cytosolic 3 alpha-HSD in intact cells, and indomethacin is capable of inhibiting this interaction.
3-Hydroxysteroid Dehydrogenases↗
Cyclical oxidation-reduction of the C3 position on bile acids catalyzed by 3 alpha-hydroxysteroid dehydrogenase. II. Studies in the prograde and retrograde single-pass, perfused rat liver and inhibition by indomethacin.
[3 beta-3H, 24-14C]Lithocholic, chenodeoxycholic, and cholic acids were administered in tracer bolus doses either prograde or retrograde in the isolated perfused rat liver. Little 3H loss from cholic acid was observed, whereas with the other bile acids, 20-40% of the administered 3H was lost in a single pass from perfusate to bile. Most of the 3H loss occurred rapidly (5 min) and was recovered as [3H]water in perfusate. Excretion of bile acids was delayed with retrograde administration, and 3H loss was more extensive. In both prograde and retrograde studies, indomethacin markedly inhibited the excretion of the bolus of bile acid into bile. Indomethacin inhibited the extraction of glycocholate (50 microM) during steady state perfusion without affecting transport maximum for excretion. At lower glycocholate concentration (5 microM), indomethacin inhibited both extraction and excretion. A greater effect was seen on excretion in the latter case, which suggests that displacement of bile acid from the cytosolic protein lead to redistribution in the hepatocyte as well as reflux into the sinusoid. These data suggest that binding of bile acids to cytosolic 3 alpha-hydroxysteroid dehydrogenases occurs extensively during hepatic transit and is important in mediating the translocation of bile acids from the sinusoidal to canalicular pole of the cell.
3-Hydroxysteroid Dehydrogenases↗
Purification of a 32.5 kDa monomeric sulfotransferase from rat liver with activity for bile acids and phenolic steroids.
Both bile acid and phenolic steroid sulfotransferase activities in rat liver cytosol have previously been identified in fractions corresponding to apparent molecular masses of 60-70 and 30-35 kDa. We purified the latter activity corresponding to a monomeric protein. Activity for bile acids and phenolic steroids co-eluted on sequential chromatography on Sephadex G-75 sf, Affigel blue, chromatofocusing and hydroxyapatite. The protein was homogeneous on SDS-PAGE (32.5 kDa).
3-Hydroxysteroid Dehydrogenases↗
Organic anion-binding by human hepatic GSH S-transferases.
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Bilirubin↗
Altered effector specificities in regulators of gene expression: TOL plasmid xylS mutants and their use to engineer expansion of the range of aromatics degraded by bacteria.
Stimulation of transcription from positively regulated promoters involves regulatory proteins that have been activated, generally as a consequence of binding low molecular weight effector molecules. To define essential structural features of effectors for one positively acting gene regulator, the xylS-encoded protein, which activates the TOL plasmid meta-cleavage pathway operon promoters, effector activities of a wide range of benzoate derivatives have been systematically analyzed, and mutant xylS-encoded proteins exhibiting altered effector specificities have been generated and characterized. Cloned mutant xylS genes were trans dominant in partial diploids containing the wild-type xylS allele and could therefore be used to effect expansion of the range of aromatic compounds completely or partially degraded by Pseudomonas bacteria. The method developed to isolate mutant xylS-encoded proteins has general applicability and could in principle be used to isolate gene regulator specificity mutants of any inducible regulatory system.
Alleles↗
Drug-induced hepatotoxicity.
Drug-induced injury to the liver can mimic any form of acute or chronic liver disease. Acute injury to the liver frequently is due to the action of cytochrome P450, which breaks down drugs into electrophiles or free radicals; these reactive metabolites can covalently bind to protein and unsaturated fatty acids or induce lipid peroxidation, respectively. These events may impair vital functions of the cell, such as maintenance of calcium homeostasis, leading to death; or hypothetically they may elicit a hypersensitivity reaction directed mainly at the liver. Glutathione and tocopherol play critical roles in cellular defense. Cholestatic disease caused by drugs results from a selective disturbance in bile secretion. Agents such as estrogens, chlorpromazine, and monohydroxy bile acids alter the chemical and physical properties of membranes, leading to impaired activity of carriers and pumps for bile acids and electrolytes. Certain drugs produce chronic liver disease that is pathologically identical to chronic active hepatitis, biliary cirrhosis, or alcoholic liver disease.
Acetaminophen↗
A single blind randomized endoscopic study comparing the effects of diflunisal and naproxen in patients with osteoarthritis.
A single blind randomized endoscopic study comparing the effects of diflunisal and naproxen on the gastric and duodenal mucosa of 34 patients with osteoarthritis was performed over a 2-week period. At the dosages utilized in the study, diflunisal produced significantly less gastric injury than naproxen, as assessed by mean gastric injury scores (p = 0.0002). Sixty-five percent of the diflunisal treated group had no evidence of gastric mucosal injury compared with 13% in the naproxen group. Moreover, treatment with diflunisal resulted in a significantly lower incidence of severe gastric injury than naproxen (p less than 0.01).
Adult↗
Comparison of the affinities of newly identified human bile acid binder and cationic glutathione S-transferase for bile acids.
The bile acid binding properties of the newly identified bile acid binder (Mr = 36,000) (FEBS Lett. 1984. 177: 31-35) and the major cationic glutathione (GSH) S-transferase (Mr = 50,000) in human liver cytosol were compared. Binding affinities were measured by the competitive displacement by bile acids of 1-anilino-8-naphthalene sulfonate (ANS) bound to the proteins and, in some cases, by direct methods of flow dialysis and equilibrium dialysis. The binding affinities for various bile acids by the human bile acid binder were 2-5 orders of magnitude greater than those by human cationic GSH S-transferase. This suggests an important physiologic role for the former protein in intracellular transfer of bile acids in human liver.
Anilino Naphthalenesulfonates↗
Identification and partial purification of a unique phenolic steroid sulphotransferase in rat liver cytosol.
Phenolic steroid sulphotransferase activity for both oestradiol and oestrone was identified in male rat liver cytosol in the 30 000-40 000 Mr fractions on gel filtration when activity was assayed at pH 5.5 (pH optimum 5.5-6.0). Activity for oestradiol but not oestrone was found in the 60 000-70 000-Mr range when assayed at pH 8.0 (pH optimum biphasic, 5.5-6.0 and 7.0-8.0). Km for oestradiol (1.3 microM) was lower than published values for hydroxysteroid sulphotransferases (15-35 microM) and previously reported oestradiol sulphotransferases (71-85 microM). At above 2 microM-oestradiol phenolic sulphotransferase activity exhibited substrate inhibition. The phenolic steroid sulphotransferase activity was found to be distinct in chromatofocusing from organic-anion-binding and bile acid-binding proteins previously identified in this Mr range. Further purification on hydroxyapatite yielded a 44-fold enriched fraction that contained two monomeric bands, Mr 32 500 and 29 500.
Animals↗
Identification and purification of a 36 kDa bile acid binder in human hepatic cytosol.
We recently purified two closely related 33 kDa proteins from rat hepatic cytosol, designated bile acid binder I and II, which selectively bind bile acids with comparable affinity as glutathione S-transferase B. This work has now been extended to human liver in which we have identified a similar cytosolic binding activity in the 30-40 kDa fraction from gel filtration. Subsequent chromatofocusing and hydroxyapatite chromatography resulted in the isolation of a homogeneous monomeric protein of 36 kDa. The binding affinity of this protein for lithocholate using the displacement of 1-anilino-8-naphthalenesulfonate (ANS) was 0.1 microM, whereas human hepatic glutathione S-transferases purified from glutathione affinity chromatography demonstrated no competitive displacement of ANS.
Amino Acids↗
Comparison of the binding affinities of five forms of rat glutathione S-transferases for bilirubin, sulfobromophthalein and hematin.
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Animals↗
Comparison of binding of thyroid hormone analogues to hepatic organic anion binding proteins.
Dv protein and ligandin are two hepatic cytosolic proteins which bind organic anions, including endogenous thyroid hormones. Binding studies were performed using the ANS displacement technique to compare the binding of a variety of thyroid hormone analogues to purified organic anion binder and ligandin. Inhibition of ANS binding by these compounds was competitive. Both proteins bound L- and D-thyroxine with comparable affinity (Kd 30-45 microM), whereas ligandin bound 3',3',5-triiodo-L-thyronine, 3',3',5-triiodo-L-thyronine and most analogues with greater affinity. Nevertheless, the order of ligand affinities for both binders was highly correlated, suggesting that the nature of the binding site on both proteins is similar. The binding affinities of these organic anion binders are 2-3 orders of magnitude lower than an hepatic cytosolic thyroid binder reported by others, suggesting that ligandin and organic anion binder may not be important in intracellular thyroid hormone transfer.
Animals↗
Quantitation and characterization of a newly described organic anion binder by radioimmunoassay.
We have recently identified a new group of proteins in rat liver cytosol which possess binding properties comparable to those of the glutathione-S-transferases, yet lack transferase activity. The bulk of organic anion binding in this fraction was associated with the tetrameric protein, designated the organic anion binder, molecular weight 34 000 (Sugiyama, Y., Yamada, T. and Kaplowitz, N. (1982) Biochim. Biophys. Acta 709, 342-352). In order to determine its tissue distribution and molecular forms, a sensitive and specific radioimmunoassay was developed. Gel filtration of rat liver and kidney cytosol demonstrated only one peak of organic anion binder-like immunoreactivity corresponding to a molecular weight of 35 000. Organic anion binder-like immunoreactivity was present in 14 separate tissues. The greatest concentration of the organic anion binder was found in the liver and kidney cytosol, where it constituted 0.5% of the cytoplasmic proteins. Similar hepatic contents were noted for female and male rats. The content of the organic anion binder in the liver and kidney were low in the fetus, but approached adult levels by 2-4 weeks of age. Treatments known to augment hepatic glutathione-S-transferase content had minimal effect on organic anion binder content. In summary, the organic anion binder is a newly recognized cytosolic binding protein, distinct from the glutathione-S-transferases, present in greatest concentration in the liver and kidney. The combination of the protein's binding properties along with its location and ontogeny suggests its possible role in intracellular organic anion transport.
Animals↗
Evidence for a common high affinity binding site on glutathione S-transferase B for lithocholic acid and bilirubin.
Binding of lithocholic acid, bilirubin, and gossypol to glutathione S-transferase B (ligandin or transferase YaYc) was compared using four methods. Tryptophan quenching revealed a single high affinity site for bilirubin and gossypol but could not be used for lithocholic acid. Both displacement of the fluorescent probe, 1-anilino-8-naphthalenesulfonate, and spectral changes induced by bilirubin binding demonstrated a common high affinity site for which all three ligands compete. Similar results were obtained by equilibrium dialysis. The dissociation constants for the binding of both bilirubin and lithocholic acid were comparable with the various methods (range 0.2-0.7 microM). Thus, lithocholic acid and bilirubin share a high affinity binding site on gluthathione S-transferase B that appears to be separate from the binding site for substrates.
Anilino Naphthalenesulfonates↗
Cytosolic bile acid binding protein in rat liver: radioimmunoassay, molecular forms, developmental characteristics and organ distribution.
Rat liver efficiently extracts bile acids from the portal blood and rapidly excretes them into bile. Little is known about the process by which bile acids traverse the liver cell from the sinusoidal to the canalicular membrane. In order to begin to define this process, we recently identified a pair of similar monomeric (33 kilodalton) cytosolic bile acid binding proteins (bile acid binders I and II, J. Biol. Chem. 1983; 258:3602-3607, Abstract). These bile acid binders have comparable binding affinities for bile acid as the YaYa and YaYc members of the family of glutathione S-transferases, the previously recognized cytoplasmic bile acid binding protein. We now report the establishment of a sensitive and specific radioimmunoassay which equally detects both bile acid binders I and II. Specificity of the antiserum was verified by the co-purification of bile acid binder immunoreactivity with the bile acid binders. Liver contained the greatest concentration of bile acid binder, where it constituted 0.33% of the total cytosolic proteins. Phenobarbital administration and lithocholate feeding had no significant effect on hepatic bile acid binder content. Examination of the ontogeny of bile acid binder revealed a rapid increase after birth to near adult levels by Day 14. In summary, we have established a sensitive radioimmunoassay for the bile acid binders. Its localization mainly in liver and its increase after birth parallel bile acid transport in the liver.
Aging↗