Biomedical Sciences, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, PEI, Canada.
Fish Physiol Biochem. 2012 Dec;38(6):1807-1813. doi: 10.1007/s10695-012-9677-2. Epub 2012 Jun 26.
Methemoglobin is oxidized hemoglobin that cannot bind to or dissociate from oxygen. In fish, it is most commonly caused by exposure to excess nitrites and can lead to abnormal swimming, buoyancy, or death. The methemoglobin concentration in mammals is determined by the balance of oxidizing agents versus reducing enzymes in erythrocytes. The objective of our studies was to characterize the enzymes that reduce methemoglobin in fish erythrocytes. Whole blood was collected from healthy rainbow trout. Methemoglobin was induced in vitro by NaNO(2) exposure. Methemoglobin reduction in controls was compared to reduction in samples with added NADH, NADPH, or NADPH and methylene blue. Rainbow trout whole blood was also fractionated into cytosol, microsomal, and mitochondria/plasma membranes/nuclei fractions. The fractions were compared for NADH-dependent cytochrome b5 reductase (CB5R) activity and for nitrite induction of methemoglobin. The CB5R activity in rainbow trout erythrocytes was compared to the CB5R activity in equine, feline, and canine erythrocytes. Rainbow trout erythrocytes had significant NADPH methemoglobin reductase activity in the presence of methylene blue (P < 0.001). The CB5R activity was greatest (P < 0.001) in the plasma membrane/mitochondria/nuclei fraction. The CB5R activity in rainbow trout erythrocytes was not significantly different than canine or equine activity but was significantly lower than feline CB5R activity (P < 0.0001). Methemoglobin in rainbow trout erythrocytes can be reduced by CB5R or NADPH-dependent methemoglobin reductase. Unlike mammalian anuclear erythrocytes, which are dependent on soluble CB5R, the nucleated RBCs of rainbow trout use membrane-bound CB5R to reduce methemoglobin.
高铁血红蛋白是不能与氧结合或解离的氧化血红蛋白。在鱼类中，高铁血红蛋白的形成通常是由于过量的亚硝酸盐暴露引起的，这可能导致异常的游泳、浮力或死亡。哺乳动物的高铁血红蛋白浓度取决于红细胞中氧化剂与还原酶的平衡。我们的研究目的是描述鱼类红细胞中还原高铁血红蛋白的酶。从健康的虹鳟鱼中采集全血。通过暴露于 NaNO2 来体外诱导高铁血红蛋白。将对照样本与添加 NADH、NADPH 或 NADPH 和亚甲蓝的样本中的高铁血红蛋白还原进行比较。还将虹鳟鱼全血分离为细胞质、微粒体和线粒体/质膜/核部分。比较 NADH 依赖性细胞色素 b5 还原酶 (CB5R) 活性和亚硝酸盐诱导高铁血红蛋白的情况。将虹鳟鱼红细胞中的 CB5R 活性与马、猫和犬红细胞中的 CB5R 活性进行比较。在亚甲蓝存在的情况下，虹鳟鱼红细胞具有显著的 NADPH 高铁血红蛋白还原酶活性 (P < 0.001)。CB5R 活性在质膜/线粒体/核部分最高 (P < 0.001)。虹鳟鱼红细胞中的 CB5R 活性与犬或马的活性没有显著差异，但明显低于猫的 CB5R 活性 (P < 0.0001)。虹鳟鱼红细胞中的高铁血红蛋白可以通过 CB5R 或 NADPH 依赖性高铁血红蛋白还原酶还原。与依赖可溶性 CB5R 的无核哺乳动物红细胞不同，虹鳟鱼有核 RBC 利用膜结合的 CB5R 还原高铁血红蛋白。
