Passamonti S, Battiston L, Sottocasa G L
Dipartimento di Biochimica Blofisica e Chimica delle Macromolecole, Università degli Saudi di Trieste, Italy.
Biochim Biophys Acta. 1997 Jan 14;1323(1):130-6. doi: 10.1016/s0005-2736(96)00181-2.
The serine protease inhibitor phenylmethylsulfonyl fluoride is shown to cause partial inhibition of bilitranslocase transport activity in rat liver plasma membrane vesicles. This condition can be fully reversed by means of pyridine-2-al-doxime methiodide, indicating that the carrier has undergone sulfonylation. Protection against inactivation is afforded by both bilirubin, the natural substrate, and nicotinic acid, but, unexpectedly, by neither sulfobromophthalein, the chromophoric substrate employed in bilitranslocase transport activity assay, nor rifamycin SV, a competitive inhibitor of sulfobromophthalein transport. From these protection experiments, the Ka for the complex of bilitranslocase with either bilirubin or nicotinic acid has been estimated to be 2.1 and 10.8 nM. respectively. Tentatively, the target for phenylmethylsulfonyl fluoride on bilitranslocase is identified as a recognition site for the physiological substrates.
丝氨酸蛋白酶抑制剂苯甲基磺酰氟被证明可部分抑制大鼠肝细胞膜囊泡中胆红素转运酶的转运活性。这种情况可通过吡啶 - 2 - 醛肟甲碘化物完全逆转，表明载体已发生磺酰化。天然底物胆红素和烟酸均可提供防止失活的保护作用，但出乎意料的是，胆红素转运酶转运活性测定中使用的发色底物磺溴酞钠和磺溴酞钠转运的竞争性抑制剂利福霉素SV均不能提供保护作用。通过这些保护实验，已估计胆红素转运酶与胆红素或烟酸复合物的解离常数分别为2.1和10.8 nM。初步确定，苯甲基磺酰氟在胆红素转运酶上的作用靶点是生理底物的识别位点。
