Quinlan D C, Li C C, Hochstadt J
J Supramol Struct. 1976;4(4):387-99. doi: 10.1002/jss.400040402.
After exposure to inosine, transport-competent plasma membrane vesicles isolated from SV-40-transformed Bal/c 3T3 cells accumulate intravesicular ribose 1-PO4 at a concentration 200-fold greater than the extravesicular concentration. An analysis of the purine nucleoside phosphorylase activity distribution in various subcellular fractions, relative to other enzyme activities, indicated the presence of plasma membrane-associated purine nucleoside phosphorylase activity. The plasma membrane vesicles appear relatively impermeable to hypoxanthine. However, hypoxanthine, which is a competitive inhibitor of the transport reaction, is the only compound tested capable of mediating efflux of already accumulated ribose 1-PO4. In addition, hypoxanthine does not result in the efflux of transported uridine which is accumulated in these membrane vesicles as uridine. Exogenous ribose 1-PO4 neither results in counterflow nor does it inhibit the original uptake reaction. The following transport reaction is proposed: uptake occurs by group translocation, mediated by membrane-localized purine nucleoside phosphorylase. The data are consistent with sites for inosine and hypoxanthine being on the outer membrane surface whereas the ribose 1-PO4 site is only on the inner surface.
用肌苷处理后，从经SV - 40转化的Bal/c 3T3细胞中分离得到的具有转运活性的质膜囊泡，其囊泡内核糖1 - 磷酸的积累浓度比囊泡外浓度高200倍。相对于其他酶活性，对各种亚细胞组分中嘌呤核苷磷酸化酶活性分布的分析表明存在与质膜相关的嘌呤核苷磷酸化酶活性。质膜囊泡对次黄嘌呤似乎相对不透性。然而，作为转运反应竞争性抑制剂的次黄嘌呤，是所测试的唯一能够介导已积累的核糖1 - 磷酸外流的化合物。此外，次黄嘌呤不会导致作为尿苷积累在这些膜囊泡中的转运尿苷外流。外源性核糖1 - 磷酸既不会导致逆流，也不会抑制最初的摄取反应。提出了以下转运反应：摄取通过基团转位发生，由膜定位的嘌呤核苷磷酸化酶介导。数据表明肌苷和次黄嘌呤的位点在外膜表面，而核糖1 - 磷酸位点仅在内表面。
