Riboflavin uptake by native Xenopus laevis oocytes.
Riboflavin uptake by native Xenopus laevis oocytes.
复制标题
天然非洲爪蟾卵母细胞摄取核黄素。
DOI：
10.1016/0005-2736(94)00232-e
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发表时间：
1995
期刊：
影响因子：
--
通讯作者：
Said,HM
中科院分区：
文献类型：
--
作者：
Dyer,DL;Said,HM
The existence of a membrane-associated uptake carrier for riboflavin (RF) is demonstrated in Xenopus oocytes. Uptake of low (0.017 μM) and high (3 μM) concentrations of RF was linear with time for up to 2 hours, and occurred with little initial binding to oocytes, and little metabolism. Uptake of RF was found to be independent of extracellular pH and Na+. The initial rate of RF uptake was saturable as a function of concentration with an apparent Kmof 0.41 ± 0.02 μM and a Vmaxof 2.86 ± 0.04 fmol/oocyte per h. Uptake of3H-RF was inhibited by unlabeled RF and by the structural analogs lumiflavin, isoriboflavin (iso-RF), 8-aminoriboflavin (8-NH2-RF), 8-hydroxyriboflavin (8-OH-RF), and lumichrome, but was not affected by flavin adenine dinucleotide (FAD), d-ribose or lumazine. Uptake of RF was significantly retarded by the metabolic inhibitor 2,4-dinitrophenol. The sulfhydryl group-modifying reagents p-chloromercuriphenylsulfonate (pCMPS), p-chloromercuribenzoate (pCMB), N-ethylmaleimide and 7-chloro-4-nitrobenz-2-oxa-1,3-diazole (NBD-Cl) all caused significant inhibition in RF uptake. The inhibitory effect of pCMPS was completely reversed by treatment of pCMPS-pretreated cells with reducing agents. While the transmembrane transport inhibitors 4-acetamido-4′-isothiocyanatostilbene-2,2′-disulfonic acid (SITS), 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS) and furosemide had no effect on RF uptake, amiloride and probenecid suppressed RF uptake in a dose-dependent fashion. Closer examination of the inhibition mediated by amiloride showed that it was competitive in nature with an apparent Kiof ∼ 1.8 mM, whereas the inhibition induced by probenecid was nonspecific. Together, these findings indicate that Xenopus oocytes possess an endogenous, specific, membrane-associated carrier-mediated uptake system for RF. The results also demonstrate the usefulness of Xenopus oocytes as a model system with which to study the RF transport event across biological membranes, which should further our present understanding of RF uptake by various vertebrate cells.
