Arion W J, Schulz L O, Walls H E
Arch Biochem Biophys. 1987 Feb 1;252(2):467-77. doi: 10.1016/0003-9861(87)90053-1.
We have examined the influence of the phenobarbital-induced proliferation of the hepatic endoplasmic reticulum (ER) on the activities of the components of the glucose-6-phosphatase system, i.e., the enzyme, the glucose-6-P translocase (T1), and the phosphate translocase (T2). Young male rats were injected ip twice daily for 4 days with 4 mg/100 g body wt of phenobarbital (PB) or an equivalent volume of saline solution. On the fifth day, the rats were killed and smooth (SER) and rough (RER) fractions of the ER were isolated from liver homogenates. Kinetic constants for glucose-6-P hydrolysis by the system and enzyme were determined and used to calculate the kinetic constants for glucose-6-P transport. T2 activity was approximated by assaying the pyrophosphatase activity at pH 6.0 in intact microsomes. Three times more SER protein was recovered from livers of PB-treated rats. PB-treatment did not alter total liver enzyme activity, but total liver T1 activity was decreased to 59% of the control value. Maximal specific activities of the system, enzyme and T1 were all reduced by PB treatment to 44% of control values in the RER and to 68% of control values in the SER. PB treatment reduced the apparent activity of T2 in RER and SER to 35 and 49% of the respective control values. In the SER from both groups of rats, T1 activity or apparent T2 activity divided by enzyme activity was about 55% of the corresponding ratio in the RER. Our analysis of these data suggests that the lower activities of T1 and T2 in the smooth ER are the results of suppression by some intrinsic component localized in the smooth membrane. Accordingly, the reduction in total liver T1 activity and, therefore, system activity in PB-treated rats reflects the redistribution of the glucose-6-P translocase from the RER to the more abundant SER membrane where it is less active. The possibility is discussed that a higher cholesterol content within the SER membrane is responsible for the lower transport activities.
我们研究了苯巴比妥诱导的肝内质网（ER）增殖对葡萄糖-6-磷酸酶系统各组分活性的影响，即该酶、葡萄糖-6-磷酸转运体（T1）和磷酸转运体（T2）。对年轻雄性大鼠每日腹腔注射两次，连续4天，每次注射4mg/100g体重的苯巴比妥（PB）或等量体积的盐溶液。在第5天，处死大鼠，从肝匀浆中分离出内质网的光滑（SER）和粗糙（RER）部分。测定该系统和酶对葡萄糖-6-磷酸水解的动力学常数，并用于计算葡萄糖-6-磷酸转运的动力学常数。通过在完整微粒体中pH 6.0条件下测定焦磷酸酶活性来估算T2活性。从PB处理组大鼠的肝脏中回收的SER蛋白是对照组的3倍。PB处理未改变肝脏总酶活性，但肝脏总T1活性降至对照值的59%。PB处理使该系统、酶和T1的最大比活性在RER中均降至对照值的44%，在SER中降至对照值的68%。PB处理使RER和SER中T2的表观活性分别降至各自对照值的35%和49%。在两组大鼠的SER中，T1活性或表观T2活性除以酶活性约为RER中相应比值的55%。我们对这些数据的分析表明，光滑内质网中T1和T2活性较低是由位于光滑膜中的某些内在成分抑制所致。因此，PB处理组大鼠肝脏总T1活性以及系统活性的降低反映了葡萄糖-6-磷酸转运体从RER重新分布到更丰富的SER膜，而在SER膜中其活性较低。文中讨论了SER膜中较高的胆固醇含量导致较低转运活性的可能性。
