Macaulay S L, Larkins R G
University of Melbourne, Department of Medicine, Royal Melbourne Hospital, Parkville, Victor, Australia.
Biochem J. 1990 Oct 15;271(2):427-35. doi: 10.1042/bj2710427.
In this study an insulin-sensitive glycophospholipid from rat adipocytes was isolated and partially characterized. A material that activated pyruvate dehydrogenase was extracted from rat adipocyte membrane supernatants. Its release was stimulated by insulin and phosphatidylinositol-specific-phospholipase C and its activity was destroyed by nitrous acid deamination. These findings suggested that insulin might stimulate breakdown of a glycophospholipid containing inositol and glucosamine, as previously reported for some other cell types [Low & Saltiel (1988) Science 239, 268-275]. A lipid that incorporated [3H]glucosamine, [3H]galactose, [3H]inositol, and [3H]myristate and whose turnover was stimulated by insulin was subsequently isolated from intact adipocytes by sequential t.l.c. using an acidic solvent system followed by a basic solvent system. The effects of insulin on turnover of the lipid in these cells were transient, with maximal effects at 1 min, and there was a typical concentration-response curve to insulin (0.07 nM-7 nM), with effects being detected over the physiological range of insulin concentrations. In contrast with studies in other cells, there was appreciable turnover of the sugar labels. The majority of the [3H]glucosamine and [3H]galactose labels were cycled through to triacylglycerol in the adipocyte. However, of that recovered in the glycophospholipid band, a major proportion (less than 40%) was recovered as the native label. Digestion of the purified molecule with phosphatidylinositol-specific phospholipase C generated a material that activated both pyruvate dehydrogenase and low-Km cyclic AMP phosphodiesterase. Impairment in insulin-stimulated breakdown of the molecule in adipocytes of streptozotocin-diabetic rats was found, consistent with the impaired insulin activation of pyruvate dehydrogenase and glucose utilization seen in this model. These findings suggest that insulin stimulates breakdown of this glycophospholipid by stimulating an insulin-sensitive phospholipase in adipocytes. This compound may serve a function as a precursor for intracellular insulin mediators.
在本研究中,从大鼠脂肪细胞中分离出一种对胰岛素敏感的糖磷脂,并对其进行了部分特性鉴定。从大鼠脂肪细胞膜上清液中提取出一种能激活丙酮酸脱氢酶的物质。其释放受到胰岛素和磷脂酰肌醇特异性磷脂酶C的刺激,其活性被亚硝酸脱氨作用破坏。这些发现表明,胰岛素可能会刺激含肌醇和葡糖胺的糖磷脂的分解,正如之前在其他一些细胞类型中所报道的那样[洛与萨尔蒂尔(1988年)《科学》239卷,268 - 275页]。随后,通过使用酸性溶剂系统接着碱性溶剂系统的连续薄层层析,从完整的脂肪细胞中分离出一种能掺入[³H]葡糖胺、[³H]半乳糖、[³H]肌醇和[³H]肉豆蔻酸且其周转受胰岛素刺激的脂质。胰岛素对这些细胞中该脂质周转的影响是短暂的,在1分钟时达到最大效应,并且对胰岛素(0.07 nM - 7 nM)有典型的浓度 - 反应曲线,在胰岛素浓度的生理范围内可检测到效应。与在其他细胞中的研究不同,糖标记有明显的周转。大部分[³H]葡糖胺和[³H]半乳糖标记在脂肪细胞中循环转化为三酰甘油。然而,在糖磷脂带中回收的部分,大部分(不到40%)以天然标记形式回收。用磷脂酰肌醇特异性磷脂酶C消化纯化的分子产生一种能激活丙酮酸脱氢酶和低Km环磷酸腺苷磷酸二酯酶的物质。发现在链脲佐菌素诱导的糖尿病大鼠的脂肪细胞中,胰岛素刺激该分子分解的能力受损,这与该模型中胰岛素激活丙酮酸脱氢酶和葡萄糖利用受损一致。这些发现表明,胰岛素通过刺激脂肪细胞中一种对胰岛素敏感的磷脂酶来刺激这种糖磷脂的分解。这种化合物可能作为细胞内胰岛素介质的前体发挥作用。