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| Name = '''Hyodeoxycholic acid'''
| ImageFile = Hyodeoxycholic_acid_acsv.svg
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'''Hyodeoxycholic acid''', also known as '''3α,6α-Dihydroxy-5β-cholan-24-oic acid''' or '''HDCA''', is a secondary [[bile acid]], one of the metabolic byproducts of [[intestinal bacteria]]. It differs from [[deoxycholic acid]] in that the 6α-[[hydroxyl]] is in the [[:File:
== Metabolism ==
In rat intestinal microflora hyodeoxycholic acid is produced by a [[gram-positive]] [[Bacilli|rod]]—termed [[HDCA-1]]—from several isomers of [[hyocholic acid]] and [[muricholic acid]].<ref name="pmid10388717">{{cite journal |author=Eyssen HJ, De Pauw G, Van Eldere J |title=Formation of hyodeoxycholic acid from muricholic acid and hyocholic acid by an unidentified gram-positive rod termed HDCA-1 isolated from rat intestinal microflora |journal=Appl. Environ. Microbiol. |volume=65 |issue=7 |pages=3158–63 |year=1999 |month=July |pmid=10388717 |pmc=91470 |doi= |url=http://aem.asm.org/cgi/pmidlookup?view=long&pmid=10388717}}</ref> In pigs with with a normal gastrointestinal flora the majority of hyodeoxycholic acid found in bile is of secondary nature, but a small amount was also found in [[Germ-
Hyodeoxycholic acid undergoes [[glucuronidation]] in human liver and kidneys.<ref name="pmid2820501">{{cite journal |author=Marschall HU, Matern H, Egestad B, Matern S, Sjövall S |title=6 alpha-glucuronidation of hyodeoxycholic acid by human liver, kidney and small bowel microsomes |journal=Biochim. Biophys. Acta |volume=921 |issue=2 |pages=392–7 |year=1987 |month=September |pmid=2820501 |doi= |url=http://linkinghub.elsevier.com/retrieve/pii/0005-2760(87)90041-5}}</ref><ref name="pmid3930288">{{cite journal |author=Parquet M, Pessah M, Sacquet E, Salvat C, Raizman A, Infante R |title=Glucuronidation of bile acids in human liver, intestine and kidney. An in vitro study on hyodeoxycholic acid |journal=FEBS Lett. |volume=189 |issue=2 |pages=183–7 |year=1985 |month=September |pmid=3930288 |doi= 10.1016/0014-5793(85)81020-6|url=http://linkinghub.elsevier.com/retrieve/pii/0014-5793(85)81020-6}}</ref> Glucuronidation of hyodeoxycholic and hyocholic acids was observed to occur extensively at the 6α-hydroxyl group, unlike primary bile acids which form 3α-hydroxy-linked [[glucuronides]]. This suggests an important pathway for the elimination of toxic and [[cholestatic]] bile acids, e.g. [[lithocholic acid|lithocholic]] and [[chenodeoxycholic acid]]s which can form hyodeoxycholic and hyocholic acids, respectively, after 6α-hydroxilation.<ref name="pmid1909626">{{cite journal |author=Matern H, Lappas N, Matern S |title=Isolation and characterization of hyodeoxycholic-acid: UDP-glucuronosyltransferase from human liver |journal=Eur. J. Biochem. |volume=200 |issue=2 |pages=393–400 |year=1991 |month=September |pmid=1909626 |doi= 10.1111/j.1432-1033.1991.tb16197.x|url=http://www3.interscience.wiley.com/resolve/openurl?genre=article&sid=nlm:pubmed&issn=0014-2956&date=1991&volume=200&issue=2&spage=393}}</ref> The enzyme family responsible for glucosidation of hyodeoxycholic acid in human liver is [[UDP-glucuronosyltransferase]]. Both the [[UGT2B4]] and [[UGT2B7]] [[isoforms]] are able to glucuronidate HDCA.<ref name="pmid8244999">{{cite journal |author=Pillot T, Ouzzine M, Fournel-Gigleux S, ''et al'' |title=Glucuronidation of hyodeoxycholic acid in human liver. Evidence for a selective role of UDP-glucuronosyltransferase 2B4 |journal=J. Biol. Chem. |volume=268 |issue=34 |pages=25636–42 |year=1993 |month=December |pmid=8244999 |doi= |url=http://www.jbc.org/cgi/pmidlookup?view=long&pmid=8244999}}</ref><ref name="pmid12527334">{{cite journal |author=Mackenzie P, Little JM, Radominska-Pandya A |title=Glucosidation of hyodeoxycholic acid by UDP-glucuronosyltransferase 2B7 |journal=Biochem. Pharmacol. |volume=65 |issue=3 |pages=417–21 |year=2003 |month=February |pmid=12527334 |doi= 10.1016/S0006-2952(02)01522-8|url=http://linkinghub.elsevier.com/retrieve/pii/S0006295202015228}}</ref> This is an example of redundancy in protection against harmful endogenous compounds provided by UGT isoforms, which present distinct but frequently overlapping [[substrate specificity]]. A common amino-acid residue that confers these two isoforms specificity to HDCA has been identified in 2006.<ref name="pmid17263731">{{cite journal |author=Barre L, Fournel-Gigleux S, Finel M, Netter P, Magdalou J, Ouzzine M |title=Substrate specificity of the human UDP-glucuronosyltransferase UGT2B4 and UGT2B7. Identification of a critical aromatic amino acid residue at position 33 |journal=[[FEBS J.]] |volume=274 |issue=5 |pages=1256–64 |year=2007 |month=March |pmid=17263731 |doi=10.1111/j.1742-4658.2007.05670.x}}</ref>
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