Polakof Sergio, Míguez Jesús M, Soengas José L
Laboratorio de Fisioloxía Animal, Departamento de Bioloxía Funcional e Ciencias da Saúde, Facultade de Bioloxía Edificio de Ciencias Experimentais, Universidade de Vigo, 36310 Vigo, Spain.
J Comp Physiol B. 2009 Jul;179(5):643-52. doi: 10.1007/s00360-009-0346-4. Epub 2009 Feb 27.
Glucokinase (GCK) is a key enzyme involved in hepatic glucose metabolism as well as in glucose homeostasis regulation. In mammals, GCK is regulated in vivo by a regulatory protein (GCKR) through a nucleus-to-cytoplasm translocation enhanced by fructose 1-phosphate and counteracted by fructose 6-phosphate. There were no previous evidences in literature regarding the presence of GCKR in livers of other vertebrates like fish and bird. Accordingly, in the present study we assessed GCKR presence in chicken, trout, carp, and goldfish hepatic homogenates. The results obtained demonstrate for the first time the presence of a GCKR-like protein in the liver of those species, with molecular weight (68 kDa) and biochemical properties similar to those described in mammals. Several of the biochemical properties of rainbow trout GCKR-like protein were closer to the mammalian model whereas those of chicken protein were specific. We also compared the presence and properties of GCKR-like protein in livers of different teleost species that exhibit different tolerances to glucose such as rainbow trout (intolerant) and goldfish and common carp (tolerant). The results showed that the most powerful GCKR-like protein was found in the most intolerant species, whereas the inhibition exerted by GCKR-like protein in tolerant species was closer to chicken than to rat. Furthermore, the response of GCKR-like protein in liver of rainbow trout fed with a diet rich in carbohydrates was compared with the rat model under extreme glycemic conditions. We found that despite trout GCKR-like protein was less active and expressed than in rat, the response against glycemic changes took place in the same direction, and the ratio GCKR-like protein:GCK was affected in a similar way.
葡萄糖激酶（GCK）是参与肝脏葡萄糖代谢以及葡萄糖稳态调节的关键酶。在哺乳动物中，GCK在体内受一种调节蛋白（GCKR）的调节，通过果糖 - 1 - 磷酸增强从细胞核到细胞质的易位，并被果糖 - 6 - 磷酸抵消。以往文献中没有关于鱼类和鸟类等其他脊椎动物肝脏中存在GCKR的证据。因此，在本研究中，我们评估了鸡、鳟鱼、鲤鱼和金鱼肝脏匀浆中GCKR的存在情况。所获得的结果首次证明了这些物种肝脏中存在一种类似GCKR的蛋白质，其分子量（68 kDa）和生化特性与哺乳动物中描述的相似。虹鳟鱼类似GCKR的蛋白质的一些生化特性更接近哺乳动物模型，而鸡的蛋白质则具有特异性。我们还比较了对葡萄糖具有不同耐受性的不同硬骨鱼物种（如虹鳟鱼（不耐受）、金鱼和鲤鱼（耐受））肝脏中类似GCKR蛋白质的存在情况和特性。结果表明，在最不耐受的物种中发现了最强有力的类似GCKR的蛋白质，而在耐受物种中类似GCKR的蛋白质所施加的抑制作用更接近鸡而不是大鼠。此外，在极端血糖条件下，将喂食富含碳水化合物饮食的虹鳟鱼肝脏中类似GCKR的蛋白质的反应与大鼠模型进行了比较。我们发现，尽管鳟鱼类似GCKR的蛋白质的活性和表达低于大鼠，但对血糖变化的反应方向相同，并且类似GCKR的蛋白质与GCK的比例受到类似的影响。
