Watkinson I A, Wilton D C, Munday K A, Akhtar M
Biochem J. 1971 Jan;121(1):131-7. doi: 10.1042/bj1210131.
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.
结果表明，100微克量的4,4'-二甲基[2-(3)H(2)]胆甾-8,14-二烯-3β-醇（IIIa）、氚代胆甾-8,14-二烯-3β-醇、4,4'-二甲基[2-(3)H(2)]胆甾-7,14-二烯-3β-醇、二氢[2-(3)H(2)]羊毛甾醇和[24-(3)H]羊毛甾醇分别被大鼠肝脏匀浆的10000g上清液转化为胆固醇，产率分别为17%、54%、6%、9.5%和24%。在有捕集剂存在的情况下，将二氢[3α-(3)H]羊毛甾醇与大鼠肝脏匀浆一起温育，发现高达38%的放射性与一个明确显示为4,4'-二甲基胆甾-8,14-二烯-3β-醇的组分相关。另一种相关化合物4,4'-二甲基胆甾-7,14-二烯-3β-醇在从二氢[3α-(3)H]羊毛甾醇温育物中捕集化合物（IIIa）的能力方面也同样有效。化合物（IIIa）进一步转化为胆固醇的机制是通过14,15-双键的还原，涉及从介质向C-15添加一个氢原子以及从NADPH的4-位向C-14添加另一个氢原子。讨论了甾醇生物合成中14α-甲基去除的两种可能机制。
