Di Giovanni Marcello, Burrone Lavinia, Chieffi Baccari Gabriella, Topo Enza, Santillo Alessandra
Dipartimento di Scienze della Vita, Seconda Università degli Studi di Napoli, via Vivaldi, Caserta, Italy.
J Exp Zool A Ecol Genet Physiol. 2010 Mar 1;313(3):137-43. doi: 10.1002/jez.585.
In this paper, we examined the distribution pattern of D-aspartic acid (D-Asp), as well as D-aspartate oxidase (D-AspO), D-amino acid oxidase (D-AAO), and L-amino acid oxidase (L-AAO) activities in different tissues of frog, Rana esculenta. High concentrations of free D-Asp were found in the testes (0.21+/-0.02 micromol/g b.w), in the liver (0.20+/-0.03 micromol/g b.w), and in the Harderian gland (HG) (0.19+/-0.03 micromol/g b.w). A higher activity of both D-AspO and D-AAO with respect to L-AAO was endogenously present in all examined frog tissues, particularly within the kidney, liver, and brain. Our in vivo experiments, consisting of i.p. injections of 2.0 micromol/g b.w. D-Asp in frogs, revealed that all examined tissues can take up and accumulate D-Asp and that this amino acid specifically triggers D-AspO activity. Indeed, no increase in both D-AAO and L-AAO was found in all frog tissues after D-Asp treatment. The optimum pH for D-AspO activity was around 8.2 and the optimum temperature was about 37 degrees C. Furthermore, its activity linearly increased with increasing D-Asp incubation times. In vitro experiments assaying the substrate specificity of D-AspO indicated that the enzyme had greater affinity for N-methyl-D-aspartate than for D-Asp and D-glutamate. This study provides evidence of the presence of free D-Asp in frog R. esculenta tissues, along with its role in triggering D-AspO activity. These findings suggest that D-AspO could play an essential role in decreasing excessive amounts of D-Asp in frog tissues, a phenomenon that, if left unchecked, could have detrimental physiological effects on the animal.
在本文中，我们研究了食用蛙不同组织中D-天冬氨酸（D-Asp）的分布模式，以及D-天冬氨酸氧化酶（D-AspO）、D-氨基酸氧化酶（D-AAO）和L-氨基酸氧化酶（L-AAO）的活性。在食用蛙的睾丸（0.21±0.02微摩尔/克体重）、肝脏（0.20±0.03微摩尔/克体重）和哈德氏腺（HG）（0.19±0.03微摩尔/克体重）中发现了高浓度的游离D-Asp。在所有检测的食用蛙组织中，尤其是在肾脏、肝脏和大脑中，内源性存在的D-AspO和D-AAO相对于L-AAO具有更高的活性。我们的体内实验包括给蛙腹腔注射2.0微摩尔/克体重的D-Asp，结果表明，所有检测的组织都能摄取和积累D-Asp，并且这种氨基酸能特异性地触发D-AspO的活性。事实上，在D-Asp处理后，所有蛙组织中的D-AAO和L-AAO均未增加。D-AspO活性的最适pH约为8.2，最适温度约为37℃。此外，其活性随D-Asp孵育时间的增加而呈线性增加。检测D-AspO底物特异性的体外实验表明，该酶对N-甲基-D-天冬氨酸的亲和力比对D-Asp和D-谷氨酸的亲和力更大。本研究提供了食用蛙组织中存在游离D-Asp及其在触发D-AspO活性中的作用的证据。这些发现表明，D-AspO可能在降低蛙组织中过量的D-Asp方面发挥重要作用，这种现象如果不加以控制，可能会对动物产生有害的生理影响。
