Takikawa H, Arai S, Yamanaka M
Department of Medicine, Teikyo University School of Medicine, Tokyo, Japan.
Arch Biochem Biophys. 1992 Nov 1;298(2):486-91. doi: 10.1016/0003-9861(92)90439-4.
Cytosolic proteins may play an important role in the intracellular transport of bile acids in enterocytes. The lithocholate binding properties of cytosolic protein from bovine small intestine were studied. Lithocholate binding was observed in the Y (45-50 kDa), Y' (30-35 kDa), and Z fractions (10-15 kDa) following gel filtration of cytosol. A Y protein with glutathione S-transferase activity (46 kDa) was purified by S-octyl-glutathione affinity chromatography and chromatofocusing (eluted at pH 7.5) of the Y fraction. Two Y' bile acid binding proteins with dihydrodiol dehydrogenase activity were partially purified from the Y' fraction by chromatofocusing and hydroxyapatite-HPLC. The lithocholate binding affinity of Y' protein (Kd < 0.35 microM) was higher than that of Y protein (Kd = 2 microM) and was comparable to that of Z protein (Kd = 0.2 microM). The binding affinity of Y protein was higher for bilirubin (Kd = 2.5 microM) than that for BSP (Kd = 200 microM). This was comparable to the binding affinity of bovine hepatic Y protein. These data indicate that Y' and Z proteins participate in the intracellular transport of bile acids from the brush border to the basolateral pole in enterocytes.
胞质蛋白可能在肠细胞内胆汁酸的转运过程中发挥重要作用。对牛小肠胞质蛋白的石胆酸结合特性进行了研究。对胞质溶胶进行凝胶过滤后，在Y（45 - 50 kDa）、Y'（30 - 35 kDa）和Z组分（10 - 15 kDa）中观察到石胆酸结合现象。通过Y组分的S - 辛基 - 谷胱甘肽亲和层析和色谱聚焦（在pH 7.5洗脱），纯化了一种具有谷胱甘肽S - 转移酶活性的Y蛋白（46 kDa）。通过色谱聚焦和羟基磷灰石 - 高效液相色谱从Y'组分中部分纯化了两种具有二氢二醇脱氢酶活性的Y'胆汁酸结合蛋白。Y'蛋白的石胆酸结合亲和力（Kd < 0.35 μM）高于Y蛋白（Kd = 2 μM），与Z蛋白（Kd = 0.2 μM）相当。Y蛋白对胆红素的结合亲和力（Kd = 2.5 μM）高于对BSP的结合亲和力（Kd = 200 μM）。这与牛肝Y蛋白的结合亲和力相当。这些数据表明，Y'和Z蛋白参与了肠细胞中胆汁酸从刷状缘到基底外侧极的细胞内转运。
