Nitrogen Excretion in Fish

9417748安德森大多数鱼以氨的形式(从蛋白质新陈代谢中)去除废物氮，氨通过鳃扩散到水中。这与大多数陆生脊椎动物不同，后者将氨转化为尿素，尿素定期储存并在尿液中排泄；这种转化的代谢途径被称为尿素循环。其中一类鱼--棘鱼(鲨鱼、溜冰鱼和银鱼)会合成并在其组织中保留高浓度的尿素，目的是在海水中保持高盐浓度的渗透平衡，以防止体内水分的损失。这些物种的尿素循环与正常排泄尿素的物种相似，但有一些显著的差异。在尿素循环中催化第一反应的酶是非常独特的。安德森博士已经确定了表达这种酶的基因的结构，以便在硬骨鱼(非板鳍鱼)中进行拟议的研究。在一些硬骨鱼的早期发育中也发现了这种独特的酶。拟议的研究将有助于确定尿素循环的这种酶的基因是否存在于所有鱼类中，以及它何时和如何表达。安德森博士的假设是，这种酶和尿素循环只在大多数鱼类的胚胎发育(非常早期的发育)期间表达。氨中毒是水产养殖业的头号问题。了解鱼类体内尿素循环酶表达的调控机制，可能为通过基因修饰鱼类表达尿素循环酶，从而提高对氨的耐受性提供机会。***

9417748 Anderson Most fish remove waste nitrogen (from protein metabolism) as ammonia, which diffuses across the gills into the water. This is in contrast to most terrestrial vertebrate animals, which convert ammonia to urea that is stored and excreted periodically in the urine; the metabolic pathway for this conversion is called the urea cycle. One group of fishes, the elasmobranchs (sharks, skates, and rays), synthesize and retain high concentrations of urea in their tissues for the purpose of maintaining an osmotic balance with the high salt concentration in sea water to prevent the loss of body water. The urea cycle in these species is analogous to that in species that normally excrete urea, but with some significant differences. The enzyme catalyzing the first reaction in the urea cycle is quite unique. Dr. Anderson has determined the structure of the gene that expresses this enzyme in order to pursue the proposed studies in teleost (non-elasmobranch) fishes. This same unique enzyme is found in the early development of some teleost fishes. The proposed studies will help to establish if the gene for this enzyme of the urea cycle is present in all fish and when and how it is expressed. Dr. Anderson's hypothesis is that this enzyme and the urea cycle are expressed only during embryogenesis (very early development) in most fish. Ammonia toxicity is the number one problem in the aquaculture industry. Understanding the mechanism of how expression of the urea cycle enzymes is regulated in fish may provide an opportunity to genetically modify fish to express the urea cycle and thus increase tolerance to ammonia. ***