Forcella Matilde, Berra Elisa, Giacchini Roberto, Parenti Paolo
Department of Environmental Sciences, University of Milano-Bicocca, Piazza della Scienza 1, 20126 Milan, Italy.
Arch Insect Biochem Physiol. 2006 Nov;63(3):110-22. doi: 10.1002/arch.20147.
Leucine transport across brush border membrane vesicles prepared from four insect species common to European freshwater streams has been characterized. The species studied were: Ephemera danica (Ephemeroptera: Ephemeridae), Isoperla grammatica (Plecoptera: Perlodidae), Hydropsyche pellucidula (Trichoptera: Hydropsychidae), and Hybomitra bimaculata (Diptera: Tabanidae). The transport differed among the studied taxa for several features, including pH and sodium dependence, substrate affinity and specificity, and efficiency. In H. pellucidula and E. danica, leucine uptake was higher at pH 7.4 than at more alkaline or acidic pH values, whereas in I. grammatica and H. bimaculata, the uptake was rather constant when pH varied from 5.0 to 7.4, then strongly decreased at pH 8.8. All but E. danica displayed a transient intravescicular leucine accumulation in the presence of sodium, suggesting the existence of a cation-leucine symport mechanism. The sodium dependence ranged according to the following order: H. pellucidula > I. grammatica > H. bimaculata > E. danica. Moreover, in H. pellucidula and I. grammatica, the sodium-dependence was stronger at pH 8.8 than at pH 7.4. In E. danica, leucine uptake was sodium-independent at all pH values. The highest value of V(max) (45.3 pmol.s(-1).mg proteins(-1)) was in E. danica, which, however, displayed the lowest affinity (K(m) 137 muM) when compared to the kinetic parameters of other taxa. The V(max) and K(m) values were: 40 and 52.5, 32.1 and 12.5, and 4.5 and 230 for H. bimaculata, H. pellucidula, and I. grammatica, respectively. The obtained results are discussed within our current knowledge of amino acid transport systems in insects.
对从欧洲淡水溪流中常见的四种昆虫物种制备的刷状缘膜囊泡中亮氨酸的转运进行了表征。所研究的物种为：丹麦蜉蝣（蜉蝣目：蜉蝣科）、细纹等蜉（襀翅目：等蜉科）、透明石蛾（毛翅目：石蛾科）和双斑瘤虻（双翅目：虻科）。在所研究的分类群中，转运在几个特征上存在差异，包括对pH和钠的依赖性、底物亲和力和特异性以及效率。在透明石蛾和丹麦蜉蝣中，pH 7.4时亮氨酸摄取高于更碱性或酸性pH值时，而在细纹等蜉和双斑瘤虻中，当pH从5.0变化到7.4时摄取相当恒定，然后在pH 8.8时强烈下降。除丹麦蜉蝣外，所有物种在有钠存在时均显示出囊泡内亮氨酸的瞬时积累，表明存在阳离子 - 亮氨酸同向转运机制。对钠的依赖性按以下顺序排列：透明石蛾>细纹等蜉>双斑瘤虻>丹麦蜉蝣。此外，在透明石蛾和细纹等蜉中，pH 8.8时对钠的依赖性强于pH 7.4时。在丹麦蜉蝣中，所有pH值下亮氨酸摄取均不依赖于钠。最大反应速度（V(max)）的最高值（45.3 pmol·s(-1)·mg蛋白质(-1)）在丹麦蜉蝣中，但与其他分类群的动力学参数相比，其亲和力最低（米氏常数（K(m)）为137 μM）。双斑瘤虻、透明石蛾和细纹等蜉的V(max)和K(m)值分别为40和52.5、32.1和12.5以及4.5和230。根据我们目前对昆虫氨基酸转运系统的了解对所得结果进行了讨论。
