Ostlund R E, Seemayer R, Gupta S, Kimmel R, Ostlund E L, Sherman W R
Metabolism Division and the Department of Psychiatry, Washington University, St. Louis, Missouri 63110, USA.
J Biol Chem. 1996 Apr 26;271(17):10073-8. doi: 10.1074/jbc.271.17.10073.
D-chiro-Inositol is an epimer of myo-inositol that is found in certain mammalian glycosylphosphatidylinositol protein anchors and inositol phosphoglycans possessing insulin-like bioactivity. In order to generate a probe for metabolic studies, D-chiro-[3-3H]inositol was synthesized by selective reduction of D-chiro-3-inosose at pH 6.5 with sodium borotritide. D-chiro-[3-3H]Inositol was taken up by HepG2 human liver cells through a saturable and stereospecific pathway in which D-chiro-inositol and myo-inositol competed equally but L-chiro-inositol was not recognized. Dd-Glucose, but not L-glucose, competed for D-chiro-[3-3H]inositol uptake over glucose concentrations of 4-28 mM. Maximum transport capacity was 717 pmol/mg cell protein/3 h with a Km value of 348 microM. Uptake was reduced by 76% when sodium was eliminated from the medium and by 94% when the experiment was performed at 0 degrees C. The new myo/D-chiro-inositol transporter is distinct from the sodium-myo-inositol co-transporter found in many tissues and accounts for all of the saturable D-chiro-inositol uptake and for a portion of the saturable low affinity myo-inositol uptake in HepG2 cells. It may allow D-chiro-inositol to be used by cells in the presence of a relatively large amount of competing myo-inositol.
D-手性肌醇是肌醇的一种差向异构体，存在于某些哺乳动物糖基磷脂酰肌醇蛋白锚和具有胰岛素样生物活性的肌醇磷酸聚糖中。为了生成用于代谢研究的探针，通过在pH 6.5下用硼氢化三钠选择性还原D-手性-3-酮糖合成了D-手性-[3-³H]肌醇。D-手性-[3-³H]肌醇通过一种可饱和且立体特异性的途径被HepG2人肝癌细胞摄取，其中D-手性肌醇和肌醇竞争能力相同，但L-手性肌醇不被识别。D-葡萄糖而非L-葡萄糖在4 - 28 mM的葡萄糖浓度范围内竞争D-手性-[3-³H]肌醇的摄取。最大转运能力为717 pmol/mg细胞蛋白/3小时，Km值为348 μM。当培养基中去除钠时摄取减少76%，当实验在0℃进行时摄取减少94%。新的肌醇/D-手性肌醇转运体不同于许多组织中发现的钠-肌醇共转运体，它解释了所有可饱和的D-手性肌醇摄取以及HepG2细胞中一部分可饱和的低亲和力肌醇摄取。它可能使D-手性肌醇在存在相对大量竞争性肌醇的情况下被细胞利用。
