Ogura M, Ayaki Y, Goto M
J Biochem. 1976 Sep;80(3):537-45. doi: 10.1093/oxfordjournals.jbchem.a131309.
In vivo and in vitro experiments with rats were carried out to investie precursor for the biosynthesis of cholic acid. When rats with a bile-fistula were given a mixture of [2-14C]mevalonate and [1,2-3H]cholesterol intravenously, the 14C:3H ratio in cholic acid in both whole homogenate and cytosol prepared from their lives was higher than that in free cholesterol in any subcellular fraction of the livers. When [2-14C] mevalonate was administered intravenously to bile-fistula rats, the specific radioactivity of free cholesterol in the hepatic microsomal fraction exceeded that in any other fraction, and the specific radioactivity of biliary cholic acid was remarkably high, exceeding that of microsomal free cholesterol. In similar experiments with [4-14C] cholesterol, the specific radioactivity of free cholesterol in the hepatic microsomal fraction exceeded that in any other subcellular fraction and the specific radioactivity of biliary cholic acid was lower than that of free cholesterol in any hepatic subcellular fraction. Tissue suspensions of rat livers in Krebs-Ringer bicarbonate (pH 7.4)-5.5 mM glucose were incubated with [2-14C]mevalonate in O2-CO2 (95:5, v/v) at 37 degrees. The specific radioactivity of free cholesterol in the microsomal fraction prepared from the incubated tissue exceeded the specific radioactivities of free cholesterol in the other subcellular fractions. The estimated specific radioactivity of taurocholate formed during the incubation was far higher than that of microsomal free cholesterol. These data indicate that hepatic microsomal free cholesterol which was newly synthesized in situ was preferentially incorporated into cholic acid.
进行了大鼠体内和体外实验以研究胆酸生物合成的前体。当给有胆瘘的大鼠静脉注射[2-¹⁴C]甲羟戊酸和[1,2-³H]胆固醇的混合物时，从其肝脏制备的全匀浆和细胞溶质中胆酸的¹⁴C:³H比值高于肝脏任何亚细胞组分中游离胆固醇的该比值。当给胆瘘大鼠静脉注射[2-¹⁴C]甲羟戊酸时，肝微粒体组分中游离胆固醇的比放射性超过任何其他组分，且胆汁胆酸的比放射性非常高，超过微粒体游离胆固醇的比放射性。在用[4-¹⁴C]胆固醇进行的类似实验中，肝微粒体组分中游离胆固醇的比放射性超过任何其他亚细胞组分，且胆汁胆酸的比放射性低于肝脏任何亚细胞组分中游离胆固醇的比放射性。将大鼠肝脏组织悬浮于含有5.5 mM葡萄糖的 Krebs-Ringer 碳酸氢盐（pH 7.4）中，在37℃于O₂-CO₂（95:5，v/v）中与[2-¹⁴C]甲羟戊酸一起孵育。从孵育组织制备的微粒体组分中游离胆固醇的比放射性超过其他亚细胞组分中游离胆固醇的比放射性。孵育过程中形成的牛磺胆酸盐的估计比放射性远高于微粒体游离胆固醇的比放射性。这些数据表明原位新合成的肝微粒体游离胆固醇优先掺入胆酸中。
