Lack L, Tantawi A, Halevy C, Rockett D
Am J Physiol. 1984 Jun;246(6 Pt 1):G745-9. doi: 10.1152/ajpgi.1984.246.6.G745.
Previous structure-activity studies of the ileal bile salt cotransport system have suggested the idea that a coulombic interaction occurs between the negative charge of the bile salt and a cationic site on the carrier. Evidence included observations that modified bile salts with uncharged, cationic, or zwitterionic side chains were poorly transported. They did interact with this system as evidenced by their abilities to inhibit transport. Another prerequisite for coulombic interaction is positional (side-chain) specificity for the anionic grouping. [14C]chenodeoxycholyl-N-ethanolamide-O-sulfate and the 3 alpha-sulfate ester of chenodeoxycholyl-N-ethanolamide were tested for their in vivo absorption from the jejunums and ileums of anesthetized guinea pigs. Active ileal transport was estimated by subtracting jejunal absorption (passive) from ileal absorption (active and passive). Translocation of the anionic SO4(-) radical from the side chain to the 3 alpha position of the steroid decreased active ileal absorption by 95%, demonstrating a positional requirement for the anionic group for optimal transport.
先前对回肠胆盐共转运系统的构效关系研究提出了这样一种观点，即胆盐的负电荷与载体上的阳离子位点之间存在库仑相互作用。证据包括以下观察结果：带有不带电荷、阳离子或两性离子侧链的修饰胆盐转运较差。它们确实与该系统相互作用，这可由它们抑制转运的能力证明。库仑相互作用的另一个先决条件是阴离子基团的位置（侧链）特异性。测试了[14C]鹅去氧胆酰-N-乙醇酰胺-O-硫酸盐和鹅去氧胆酰-N-乙醇酰胺的3α-硫酸酯在麻醉豚鼠空肠和回肠中的体内吸收情况。通过从回肠吸收（主动和被动）中减去空肠吸收（被动）来估计回肠的主动转运。阴离子SO4(-)基团从侧链转移到甾体的3α位置使回肠的主动吸收降低了95%，这表明阴离子基团对于最佳转运存在位置要求。
