Battaglia E, Nowell S, Drake R R, Mizeracka M, Berg C L, Magdalou J, Fournel-Gigleux S, Gollan J L, Lester R, Radominska A
Department of Internal Medicine, University of Arkansas for Medical Sciences, Little Rock 72204, USA.
Biochim Biophys Acta. 1996 Sep 4;1283(2):223-31. doi: 10.1016/0005-2736(96)00098-3.
Previous studies have documented the presence of protein-mediated transport of UDP-glucuronic acid (UDP-GlcUA) in rat liver endoplasmic reticulum (ER). Measurement of uptake at varying concentrations of high specific activity [beta-32P]UDP-GlcUA has revealed the presence of a two component UDP-GlcUA transporting system. Transport at low substrate concentrations occurred predominantly via a high affinity component (K(m) = 1.6 microM), whereas a low affinity component (K(m) = 38 microM) predominated at high substrate concentrations. The K(m) for the high affinity system is in agreement with that previously published, while the low affinity component is a new finding. The uptake of UDP-GlcUA was temperature-sensitive, time dependent, and saturable for both components. The high affinity transport was affected by trans-stimulation and cis-inhibition by UDP-N-acetylglucosamine (UDP-GlcNAc); however, the same concentrations of UDP-GlcNAc had less effect on the low affinity system. In order to further study the two transport components, various inhibitors of anion transport carriers were tested. The high affinity component was strongly inhibited by 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS) and furosemide, while the low affinity system was less sensitive to these reagents. Dose-dependent inhibition by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) was found for both transport systems. Probenecid was found to be a weak inhibitor of both components of the UDP-GlcUA uptake. Finally, the major metabolite of 3'-azido-3'-deoxythymidine, 3'-azido-3'-deoxythymidine monophosphate (AZTMP), was able to inhibit the uptake of UDP-GlcUA by both components. The results indicate the presence of two carrier-mediated UDP-glucuronic acid transporting components in rat liver ER.
先前的研究已证明大鼠肝脏内质网（ER）中存在蛋白质介导的UDP-葡萄糖醛酸（UDP-GlcUA）转运。在不同浓度的高比活度[β-32P]UDP-GlcUA下测量摄取量，揭示了存在一个双组分UDP-GlcUA转运系统。低底物浓度下的转运主要通过高亲和力组分（K(m)=1.6 microM）进行，而高底物浓度下低亲和力组分（K(m)=38 microM）占主导。高亲和力系统的K(m)与先前发表的一致，而低亲和力组分是一个新发现。UDP-GlcUA的摄取对温度敏感、具有时间依赖性，且两个组分均具有饱和性。高亲和力转运受到UDP-N-乙酰葡糖胺（UDP-GlcNAc）的反式刺激和顺式抑制的影响；然而，相同浓度的UDP-GlcNAc对低亲和力系统的影响较小。为了进一步研究这两个转运组分，测试了各种阴离子转运载体抑制剂。高亲和力组分受到4-乙酰氨基-4'-异硫氰酸基芪-2,2'-二磺酸（SITS）和呋塞米的强烈抑制，而低亲和力系统对这些试剂不太敏感。发现4,4'-二异硫氰酸基芪-2,2'-二磺酸（DIDS）对两个转运系统均有剂量依赖性抑制作用。丙磺舒被发现是UDP-GlcUA摄取两个组分的弱抑制剂。最后，3'-叠氮-3'-脱氧胸苷的主要代谢产物3'-叠氮-3'-脱氧胸苷单磷酸（AZTMP）能够抑制两个组分对UDP-GlcUA的摄取。结果表明大鼠肝脏内质网中存在两个载体介导的UDP-葡萄糖醛酸转运组分。
