{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,25]],"date-time":"2025-10-25T18:51:36Z","timestamp":1761418296447},"reference-count":33,"publisher":"Wiley","issue":"1","license":[{"start":{"date-parts":[[2005,1,20]],"date-time":"2005-01-20T00:00:00Z","timestamp":1106179200000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":["onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["J Eukaryotic Microbiology"],"published-print":{"date-parts":[[2005,2]]},"abstract":"<jats:p><jats:bold>Abstract. <\/jats:bold> Live <jats:italic>Tetrahymena thermophila<\/jats:italic> transforms exogenous cholesterol into 7,22\u2010<jats:italic>bis<\/jats:italic>, dehydrocholesterol (DHC) by desaturation at positions C7(8) and C22(23) of the cholesterol moiety. In this first report on expression, isolation, characterization, and reconstitution of <jats:italic>Tetrahymena'<\/jats:italic>s cholesterol desaturases in cell\u2010free extracts, we describe conditions for increasing the expression of both desaturases based on the addition of specific sterols to the culture medium. Reactions performed in vitro, with isolated microsomes, yield only the mono\u2010unsaturated derivatives, 7\u2010DHC and\/or 22\u2010DHC. However, selectivity towards one product can be improved with the addition of specific compounds: \u03b2\u2010mercaptoethanol inhibited C22(23) desaturase activity completely, while ethanol selectively increased this activity. Detergent\u2010solubilized microsomes showed no desaturase activity, but partial restoration could be achieved with addition of dilauroyl\u2010phosphatidylcholine liposomes (25%). Both cholesterol desaturases require molecular oxygen and cytochrome <jats:italic>b<\/jats:italic><jats:sub>5<\/jats:sub>. NADH or NADPH can serve as reduced cofactors, albeit with different efficiency, delivered by reductases present in the microsomal fraction. Azide and cyanide, but not azole compounds, inhibited these desaturases, suggesting a key role for cytochrome <jats:italic>b<\/jats:italic><jats:sub>5<\/jats:sub> in these reactions.<\/jats:p>","DOI":"10.1111\/j.1550-7408.2005.3279rr.x","type":"journal-article","created":{"date-parts":[[2005,2,9]],"date-time":"2005-02-09T19:52:00Z","timestamp":1107978720000},"page":"61-67","update-policy":"http:\/\/dx.doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":15,"title":["Characterization and Properties of Cholesterol Desaturases from the Ciliate <i>Tetrahymena thermophila<\/i>"],"prefix":"10.1111","volume":"52","author":[{"given":"Alejandro D.","family":"Nusblat","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Luciana","family":"Mu\u00f1oz","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"German A.","family":"Valcarce","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Clara B.","family":"Nudel","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"311","published-online":{"date-parts":[[2005,1,20]]},"reference":[{"key":"e_1_2_6_2_1","doi-asserted-by":"publisher","DOI":"10.1042\/bj1420057"},{"key":"e_1_2_6_3_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1550-7408.1981.tb02818.x"},{"key":"e_1_2_6_4_1","doi-asserted-by":"publisher","DOI":"10.1139\/y59-099"},{"key":"e_1_2_6_5_1","doi-asserted-by":"publisher","DOI":"10.1007\/s11745-997-0026-z"},{"key":"e_1_2_6_6_1","doi-asserted-by":"publisher","DOI":"10.1007\/BF02533747"},{"key":"e_1_2_6_7_1","doi-asserted-by":"crossref","first-page":"2325","DOI":"10.1016\/S0021-9258(19)78229-5","article-title":"The conversion of cholesterol to \u03945,7,22\u2010cholestatrien\u20103\u03b2\u2010ol by Tetrahymena pyriformis","volume":"244","author":"Conner R.","year":"1966","journal-title":"J. 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