Panini S R, Lehrer G, Rogers D H, Rudney H
J Lipid Res. 1979 Sep;20(7):879-89.
3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase, E.C. 1.1.1.34), the major rate-limiting enzyme of the sterol biosynthetic pathway, was studied in ileal epithelial cells isolated in a villus-to-crypt gradient according to Weiser (Weiser, M. M. 1973. J. Biol. Chem, 248:2536-2541). Alkaline phosphatase (E.C. 3.1.3.1) served as a marker for the mature villus cells. Protease effects on activity determinations were negligible. The intracellular location of HMG-CoA reductase could not be precisely determined. The activity of ileal reductase was predominantly associated with the less differentiated lower villus and crypt cells, while the reverse gradient occurred with alkaline phosphatase. This distribution of enzymes persisted in both fed and fasted rats injected with control saline-phosphate, although fasting decreased total reductase units in the ileum by 86% in 72 hr. Treatment with cholestyramine and with 4-aminopyrazolo[3,4-d]pyrimidine (APP) enhanced reductase activity in ileal cells. The percent stimulation in both cases was higher in the upper villus cells than in the crypt cells, leading to abolition of the gradient in enzyme activity. However, APP treatment caused a 98% loss in total alkaline phosphatase units and a 55% loss in total epithelial cell protein in 72 hr. Thus, there was no increase in total reductase units. These data show that APP affects ileal cell metabolism directly. Furthermore, it appears that the regulation of sterol synthesis in the intestinal mucosa, via HMG-CoA reductase, involves a complex interplay of the effects exerted by the level of alimentation, the enterohepatic circulation of bile, and the levels of plasma lipoproteins.
3-羟基-3-甲基戊二酰辅酶A还原酶（HMG-CoA还原酶，E.C. 1.1.1.34）是固醇生物合成途径中的主要限速酶，我们根据韦泽（韦泽，M.M. 1973.《生物化学杂志》，248:2536 - 2541）的方法，对沿绒毛至隐窝梯度分离的回肠上皮细胞中的该酶进行了研究。碱性磷酸酶（E.C. 3.1.3.1）作为成熟绒毛细胞的标志物。蛋白酶对活性测定的影响可忽略不计。HMG-CoA还原酶的细胞内定位无法精确确定。回肠还原酶的活性主要与分化程度较低的绒毛下部和隐窝细胞相关，而碱性磷酸酶则呈现相反的梯度分布。在注射对照盐溶液 - 磷酸盐的喂食和禁食大鼠中，这种酶的分布均持续存在，尽管禁食在72小时内使回肠中总还原酶单位减少了86%。用消胆胺和4-氨基吡唑并[3,4 - d]嘧啶（APP）处理可增强回肠细胞中的还原酶活性。在这两种情况下，上部绒毛细胞中的刺激百分比均高于隐窝细胞，导致酶活性梯度消失。然而，APP处理在72小时内导致总碱性磷酸酶单位损失98%，总上皮细胞蛋白损失55%。因此，总还原酶单位没有增加。这些数据表明APP直接影响回肠细胞代谢。此外，似乎通过HMG-CoA还原酶对肠道黏膜中固醇合成的调节涉及营养水平、胆汁的肠肝循环以及血浆脂蛋白水平所施加影响的复杂相互作用。
