Einarsson K, Angelin B, Ewerth S, Nilsell K, Björkhem I
J Lipid Res. 1986 Jan;27(1):82-8.
The present work describes an accurate assay of the rate-limiting enzyme in bile acid synthesis, the cholesterol 7 alpha-hydroxylase, in human liver. The assay is based on isotope dilution-mass spectrometry, and endogenous microsomal cholesterol is used as the only substrate for the enzyme. Operative liver biopsies were obtained from patients undergoing elective cholecystectomy under highly standardized conditions. In ten gallstone patients, the enzyme activity of the microsomal fraction averaged 9.6 +/- 1.4 (mean +/- SEM) pmol X min-1 X mg protein-1 corresponding to a daily synthesis of about 0.5 mmol of bile acids. Three cholestyramine-treated patients displayed a four-fold higher enzyme activity. No evidence was obtained supporting the concept that the cholesterol 7 alpha-hydroxylase is modulated by phosphorylation-dephosphorylation.
本研究描述了一种对人肝脏中胆汁酸合成限速酶——胆固醇7α-羟化酶的精确测定方法。该测定基于同位素稀释质谱法，内源性微粒体胆固醇用作该酶的唯一底物。在高度标准化条件下，对接受择期胆囊切除术的患者进行手术肝活检。在10例胆结石患者中，微粒体部分的酶活性平均为9.6±1.4（平均值±标准误）pmol·min⁻¹·mg蛋白⁻¹，相当于每日约合成0.5 mmol胆汁酸。3例接受消胆胺治疗的患者酶活性高4倍。未获得支持胆固醇7α-羟化酶受磷酸化-去磷酸化调节这一概念的证据。
