Shiozaki H, Yoshioka M, Miura S, Imaeda H, Morita A, Asakura H, Tsuchiya M, Ishii H
Department of Internal Medicine, School of Medicine, Keio University, Tokyo, Japan.
Dig Dis Sci. 1995 Jun;40(6):1193-8. doi: 10.1007/BF02065523.
The mechanisms whereby the conjugated bile salts regulate the activities of the brush border membrane hydrolases and its physiological significance were investigated in rat small intestine, and comparisons were made with the action of pancreatic protease. Rat brush border membrane proteins were metabolically labeled with [35S]methionine, and isolated brush border membrane was incubated with taurocholate or pancreatic elastase. The activity of solubilized hydrolases was assayed and the molecular forms of the hydrolases were examined by SDS-PAGE. The activity and protein bands of alkaline phosphatase and sucrase-isomaltase were solubilized by taurocholate, while alkaline phosphatase was not solubilized by elastase. Solubilized sucrase-isomaltase molecules were proteolytically degraded by elastase, whereas the intact molecule of sucrase-isomaltase was solubilized by taurocholate. Next the physiological role of bile salts in brush border membrane hydrolase turnover were investigated using metabolic labeling of brush border membrane hydrolase and immunoprecipitation in biliary diversion rats. After three days of biliary diversion, a significant increase in alkaline phosphatase activity was observed. Although synthesis of alkaline phosphatase in biliary diversion rats was similar to that observed in control rats, biliary diversion rats showed 1.5-fold slower turnover of alkaline phosphatase when compared with control rats. These results suggest that conjugated bile salts in the intestinal lumen may cause a rapid turnover of brush border membrane hydrolases, which may be increased by the enhanced enzyme degradation. The mechanisms for the enhanced degradation appeared to be solubilization of hydrolases caused by the detergent activity of bile salts. Therefore, conjugated bile salts may play an important physiological role in the regulation of expression of the protease-resistant enzymes such as alkaline phosphatase.
在大鼠小肠中研究了结合型胆盐调节刷状缘膜水解酶活性的机制及其生理意义，并与胰蛋白酶的作用进行了比较。用[35S]甲硫氨酸对大鼠刷状缘膜蛋白进行代谢标记，将分离的刷状缘膜与牛磺胆酸盐或胰弹性蛋白酶一起孵育。测定可溶性水解酶的活性，并通过SDS-PAGE检测水解酶的分子形式。碱性磷酸酶和蔗糖酶-异麦芽糖酶的活性和蛋白条带可被牛磺胆酸盐溶解，而碱性磷酸酶不能被弹性蛋白酶溶解。可溶性蔗糖酶-异麦芽糖酶分子可被弹性蛋白酶蛋白水解降解，而蔗糖酶-异麦芽糖酶的完整分子可被牛磺胆酸盐溶解。接下来，利用刷状缘膜水解酶的代谢标记和胆道引流大鼠的免疫沉淀法，研究了胆盐在刷状缘膜水解酶周转中的生理作用。胆道引流三天后，观察到碱性磷酸酶活性显著增加。虽然胆道引流大鼠碱性磷酸酶的合成与对照大鼠相似，但与对照大鼠相比，胆道引流大鼠碱性磷酸酶的周转速度慢1.5倍。这些结果表明，肠腔内的结合型胆盐可能导致刷状缘膜水解酶的快速周转，这可能因酶降解增强而增加。降解增强的机制似乎是胆盐的去污剂活性导致水解酶溶解。因此，结合型胆盐可能在调节碱性磷酸酶等抗蛋白酶的酶的表达中发挥重要的生理作用。
