The formation and reduction of the 14,15-double bond in cholesterol biosynthesis.
It was shown that 100mug quantities of 4,4'-dimethyl[2-(3)H(2)]cholesta-8,14-dien-3beta-ol (IIIa), tritiated cholesta-8,14-dien-3beta-ol, 4,4'-dimethyl[2-(3)H(2)]cholesta-7,14-dien-3beta-ol, dihydro[2-(3)H(2)]lanosterol and [24-(3)H]lanosterol were converted by a 10000g supernatant of rat liver homogenate into cholesterol in 17%, 54%, 6%, 9.5% and 24% yields respectively. From an incubation of dihydro[3alpha-(3)H]lanosterol with a rat liver homogenate in the presence of a trap up to 38% of the radioactivity was found to be associated with a fraction that was unambiguously shown to be 4,4'-dimethylcholesta-8,14-dien-3beta-ol. Another related compound, 4,4'-dimethylcholesta-7,14-dien-3beta-ol was also shown to be equally effective in its ability to trap compound (IIIa) from an incubation of dihydro[3alpha-(3)H]lanosterol. The mechanism of the further conversion of the compound (IIIa) into cholesterol occurred by the reduction of the 14,15-double bond and involved the addition of a hydrogen atom from the medium to C-15 and another from the 4-position of NADPH to C-14. Two possible mechanisms for the removal of the 14alpha-methyl group in sterol biosynthesis are discussed.
D000818:Animals; D002498:Centrifugation; D002776:Cholestanes / Q000096:biosynthesis / Q000378:metabolism; D002784:Cholesterol / Q000096:biosynthesis*; D002845:Chromatography; D006859:Hydrogen; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D009532:Nickel; D010084:Oxidation-Reduction; D051381:Rats; D013261:Sterols / Q000096:biosynthesis / Q000378:metabolism; D014316:Tritium
D002776:Cholestanes; D013261:Sterols; D014316:Tritium; D009249:NADP; D009532:Nickel; D006859:Hydrogen; D002784:Cholesterol