Biotransformation of Bile Acids and Cholesterol by the Intestinal Microflora

Hylemon, Phillip B.; Glass, Thomas L.

doi:10.1016/b978-0-12-341280-5.50015-x

Cited by 65 publications

(26 citation statements)

References 74 publications

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“…During their enterohepatic circulation, these primary bile acids are transformed into a variety of metabolites by the intestinal microflora (9,10). The metabolism of bile acids by the intestinal microflora is limited by the constraints inherent in the strictly anaerobic environments of the colon.…”

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Evidence for a multigene family involved in bile acid 7-dehydroxylation in Eubacterium sp. strain VPI 12708

et al. 1988

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Eubacterium sp. strain VPI 12708 is a human intestinal isolate which has an inducible bile acid 7-dehydroxylation activity. At least two cholic acid-induced polypeptides, with molecular masses of 27,000 and 45,000 daltons, respectively, coelute with bile acid 7-dehydroxylation activity. The 45,000-dalton polypeptide appears to be encoded by a cholic acid-induced mRNA species of greater than 6 kilobases, which suggests that the gene coding for this polypeptide is part of a larger operon. A gene has been cloned which flanks the gene encoding the 45,000-dalton polypeptide, in the upstream (5') direction. This gene appears to encode a second 27,000-dalton polypeptide. The gene bears striking homology at both the nucleotide (80%) and deduced amino acid sequence (89%) levels with the gene which encodes the 27,000-dalton polypeptide that has been shown previously to be involved in the bile acid 7-dehydroxylation reaction sequence. The implications of this homology and the possible function(s) of the two homologous genes in bile acid 7-dehydroxylation are discussed. Evidence is presented which suggests that the two homologous genes involved in bile acid 7-dehydroxylation may be part of a larger multigene family in Eubacterium sp. strain VPI 12708.

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Evidence for a multigene family involved in bile acid 7-dehydroxylation in Eubacterium sp. strain VPI 12708

et al. 1988

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“…Bile acids conjugated via an amide bond to either taurine or glycine in the liver are released into the small intestine in those salt forms (11). The salts are modified by numerous microbial biotransformations in the intestines (11).…”

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“…The salts are modified by numerous microbial biotransformations in the intestines (11). In the first of such reactions, the amide bond is hydrolyzed to release free amino acid and the primary bile acid.…”

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Characterization and purification of bile salt hydrolase from Lactobacillus sp. strain 100-100

Lundeen

Savage

1990

J Bacteriol

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We have characterized and purified the bile salt hydrolase from Lactobacillus sp. strain 100-100. Bile salt hydrolase from cells of the strain was purified with column and high-performance liquid chromatography. The activity was assayed in whole cells and cell-free extracts with either a radiochemical assay involving ['4C]taurocholic acid or a nonradioactive assay involving trinitrobenzene sulfonate. The activity was detectable only in stationary-phase cells. Within 20 min after conjugated bile acids were added to stationary-phase cultures of strain 100-100, the activity in whole cells increased to levels three-to fivefold higher than in cells from cultures grown in medium free of bile salts. In cell-free extracts, however, the activity was about equal, 1.41 and 1.53 ,umol/min per mg of protein, respectively, whether or not the cells have been grown with bile salts present. When supernatant solutions from cultures grown in medium containing taurocholic acid were used to suspend cells grown in medium free of the bile salt, the bile salt hydrolase activity detected in whole cells increased two-to threefold. Two forms of the hydrolase were purified from the cells and designated hydrolases A and B. They eluted from anion-exchange high-performance liquid chromatography in two sets of fractions, A at 0.15 M NaCl and B at 0.18 M NaCl. Their apparent molecular weights in nondenaturing polyacrylamide gel electrophoresis were 115,000 and 105,000, respectively. However, discrepancies existed in the apparent molecular weights and number of peptides detected in sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the two forms. Both had similar substrate specificities, highest on taurodeoxycholic and glycocholic acid, and pH optima between 3.8 and 4.5. The kinetic properties were also similar, with Vmaxs of 17 and 53 ,Lmol/min per mg of protein and Kms of 0.76 and 0.95 mM taurocholic acid for A and B, respectively.

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“…During their passage through the intestinal lumen, the bile acids are exposed to the indigenous intestinal microflora, many of which can modify the bile acids. These modifications include hydrolysis of the amide bond of conjugated bile acids, oxidation or reduction of hydroxy moieties, and the reductive 7-dehydroxylation of the primary bile acids (15,19).…”

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Characterization of the baiH gene encoding a bile acid-inducible NADH:flavin oxidoreductase from Eubacterium sp. strain VPI 12708

1993

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A cholate-inducible, NADH-dependent flavin oxidoreductase from the intestinal bacterium Eubacterium sp. strain VPI 12708 was purified 372-fold to apparent electrophoretic homogeneity. The subunit and native molecular weights were estimated to be 72,000 and 210,000, respectively, suggesting a homotrimeric organization. Three peaks of NADH:flavin oxidoreductase activity (forms I, H, and III) eluted from a DEAE-high-performance liquid chromatography column. Absorption spectra revealed that purified form III, but not form I, contained bound flavin, which dissociated during purification to generate form I. Enzyme activity was inhibited by sulfhydryl-reactive compounds, acriflavine, o-phenanthroline, and EDTA. Activity assays and Western blot (immunoblot) analysis confirmed that expression of the enzyme was cholate inducible. The first 25 N-terminal amino acid residues of purified NADH:flavin oxidoreductase were determined, and a corresponding oligonucleotide probe was synthesized for use in cloning of the associated gene, baiH. Restriction mapping, sequence data, and RNA blot analysis suggested that the baiH gene was located on a previously described, cholate-inducible operon 210 kb long. The baiH gene encoded a 72,006-Da polypeptide containing 661 amino acids. The deduced amino acid sequence of the baiH gene was homologous to that of NADH oxidase from Thermoanaerobium brockii, trimethylamine dehydrogenase from methylotrophic bacterium W3A1, Old Yellow Enzyme from Saccharomyces carisbergensis, and the product of the baiC gene ofEubacterium sp. strain VPI 12708, located upstream from the baiH gene in the cholate-inducible operon. Alignment of these five sequences revealed potential ligands for an iron-sulfur cluster, a putative fiavin adenine dinucleotide-binding domain, and two other well-conserved domains of unknown function.

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Biotransformation of Bile Acids and Cholesterol by the Intestinal Microflora

Cited by 65 publications

References 74 publications

Evidence for a multigene family involved in bile acid 7-dehydroxylation in Eubacterium sp. strain VPI 12708

Evidence for a multigene family involved in bile acid 7-dehydroxylation in Eubacterium sp. strain VPI 12708

Characterization and purification of bile salt hydrolase from Lactobacillus sp. strain 100-100

Characterization of the baiH gene encoding a bile acid-inducible NADH:flavin oxidoreductase from Eubacterium sp. strain VPI 12708

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