Stremmel W, Lotz G, Strohmeyer G, Berk P D
J Clin Invest. 1985 Mar;75(3):1068-76. doi: 10.1172/JCI111769.
The mechanisms by which FFA are absorbed by the gut are unclear. To examine these processes, binding of [14C]oleate to isolated rat jejunal microvillous membranes (MVM) was studied in vitro. When [14C]oleate alone or compounded with bovine serum albumin at various molar ratios was incubated with MVM aliquots, binding was time- and temperature-dependent, inhibitable by addition of excess cold oleate, and decreased by heat denaturation or trypsin digestion of the membranes. When [14C]oleate binding to heat denatured MVM, which increased continuously as a function of the free oleate concentration and was taken as a measure of nonspecific binding, was subtracted from total binding to native MVM, a curve suggestive of saturable specific binding was observed. In contrast to fatty acids, there was no specific binding of [14C]taurocholate or [35S]sulfobromophthalein to jejunal MVM. After MVM solubilization with 1% Triton X-100, affinity chromatography over oleate-agarose and elution with 7 M urea yielded a single 40,000-mol-wt protein. This Sudan Black/periodic acid-Schiff-stain-negative protein co-chromatographed on Sephadex G-100 with [14C]oleate, [14C]palmitate, [14C]arachidonate, and [14C]linoleate, but not with the [14C]oleate ester of cholesterol, [14C]phosphatidylcholine, [14C]taurocholate, or [35S]sulfobromophthalein. A rabbit antibody to the previously reported hepatic membrane fatty acid binding protein (FABP) gave a single line of immunologic identity between the FABPs of rat jejunum and rat liver membrane. It inhibited the binding of [14C]oleate to native MVM but not heat denatured MVM, and, in immunohistochemical studies, demonstrated the presence of the FABP in the apical and lateral portions of the brush border cells of the jejunum, but not on the luminal surface of esophagus or colon. These data are compatible with the hypothesis that a specific FABP plays a role in fatty acid absorption from the gut.
游离脂肪酸（FFA）被肠道吸收的机制尚不清楚。为了研究这些过程，我们在体外研究了[14C]油酸与分离的大鼠空肠微绒毛膜（MVM）的结合情况。当单独的[14C]油酸或以各种摩尔比与牛血清白蛋白混合后与MVM等分试样孵育时，结合具有时间和温度依赖性，可被加入过量的冷油酸所抑制，并且通过膜的热变性或胰蛋白酶消化而降低。当从与天然MVM的总结合中减去与热变性MVM的[14C]油酸结合（其随游离油酸浓度持续增加并被视为非特异性结合的量度）时，观察到一条提示可饱和特异性结合的曲线。与脂肪酸不同，[14C]牛磺胆酸盐或[35S]磺溴酞钠与空肠MVM没有特异性结合。在用1% Triton X - 100溶解MVM后，通过油酸 - 琼脂糖亲和层析并用7 M尿素洗脱，得到一种单一的40,000道尔顿分子量的蛋白质。这种苏丹黑/过碘酸 - 希夫染色阴性的蛋白质在Sephadex G - 100上与[14C]油酸、[14C]棕榈酸、[14C]花生四烯酸和[14C]亚油酸共层析，但不与胆固醇的[14C]油酸酯、[14C]磷脂酰胆碱、[14C]牛磺胆酸盐或[35S]磺溴酞钠共层析。针对先前报道的肝细胞膜脂肪酸结合蛋白（FABP）的兔抗体在大鼠空肠和大鼠肝细胞膜的FABP之间给出了单一的免疫同一性条带。它抑制了[14C]油酸与天然MVM的结合，但不抑制与热变性MVM的结合，并且在免疫组织化学研究中，证明FABP存在于空肠刷状缘细胞的顶端和侧面部分，但不存在于食管或结肠的腔表面。这些数据与特定的FABP在肠道脂肪酸吸收中起作用的假设相符。
