Mithieux G, Bordeto J C, Minassian C, Ajzannay A, Mercier I, Riou J P
Institut National de la Santé et de la Recherche Médicale, Unité 197, Faculté de Médecine A. Carrel, Lyon, France.
Eur J Biochem. 1993 Apr 1;213(1):461-6. doi: 10.1111/j.1432-1033.1993.tb17782.x.
The effect of arachidonic acid (delta 4Ach) on liver glucose-6-phosphatase (Glc6Pase) has been studied in vitro using untreated and detergent-treated microsomes prepared from fed and 48-h-fasted normal rats and from streptozotocin-induced diabetic rats. Glc6Pase of both untreated and detergent-treated microsomes (60 micrograms protein/ml) is inhibited by delta 4Ach in a dose-dependent manner between 10-100 microM. The inhibition is very rapid and does not depend on preincubation of microsomes in the presence of delta 4Ach. It does depend on the concentration of microsomal membranes and on the concentration of glucose 6-phosphate: it is more pronounced at low Glc6P concentrations than at high. As a consequence, the enzyme displays sigmoidal kinetics in the presence of delta 4Ach. Hill coefficients (equal to 1 in the control experiments) of about 1.4 were determined in the presence of 50 microM delta 4Ach, indicating a clear positive cooperative dependency of the Glc6Pase upon its substrate in the presence of delta 4Ach. The delta 4Ach inhibition is fully reversible in the presence of bovine serum albumin. The inhibition does not depend on the metabolism of delta 4Ach through the prostaglandin synthase (cyclooxygenase) or arachidonate 12-lipoxygenase pathways since it is not affected by indomethacin and nordihydroguaiaretic acid. Several other unsaturated fatty acids are able to inhibit the enzyme within the same concentration range. In contrast, saturated fatty acids, the arachidonic acid methyl ester and numerous other lipid compounds containing esterified unsaturated fatty acids do not inhibit Glc6Pase within the same concentration range. The enzyme of fed rats was inhibited in the same manner as the enzyme of 48-h-fasted rats. However, Glc6Pase of untreated microsomes from diabetic rats was less inhibitable by delta 4Ach than the Glc6Pase of normal rats. This difference does not persist after solubilization of the membrane lipids by detergent treatment.
已使用从喂食和禁食48小时的正常大鼠以及链脲佐菌素诱导的糖尿病大鼠制备的未处理和经去污剂处理的微粒体，在体外研究了花生四烯酸（δ4Ach）对肝脏葡萄糖-6-磷酸酶（Glc6Pase）的影响。在10-100微摩尔之间，未处理和经去污剂处理的微粒体（60微克蛋白质/毫升）中的Glc6Pase均被δ4Ach以剂量依赖性方式抑制。这种抑制非常迅速，并且不依赖于微粒体在δ4Ach存在下的预孵育。它确实取决于微粒体膜的浓度和葡萄糖6-磷酸的浓度：在低Glc6P浓度下比在高浓度下更明显。因此，该酶在δ4Ach存在下表现出S形动力学。在存在50微摩尔δ4Ach的情况下，测定的希尔系数（在对照实验中等于1）约为1.4，表明在δ4Ach存在下，Glc6Pase对其底物具有明显的正协同依赖性。在牛血清白蛋白存在下，δ4Ach抑制作用是完全可逆的。该抑制不依赖于δ4Ach通过前列腺素合酶（环氧化酶）或花生四烯酸12-脂氧合酶途径的代谢，因为它不受吲哚美辛和去甲二氢愈创木酸的影响。其他几种不饱和脂肪酸能够在相同浓度范围内抑制该酶。相比之下，饱和脂肪酸、花生四烯酸甲酯和许多其他含有酯化不饱和脂肪酸的脂质化合物在相同浓度范围内不抑制Glc6Pase。喂食大鼠的酶与禁食48小时大鼠的酶受到相同方式的抑制。然而，糖尿病大鼠未处理微粒体中的Glc6Pase比正常大鼠的Glc6Pase对δ4Ach的抑制作用更不敏感。在用去污剂处理使膜脂溶解后，这种差异不再存在。
