Esbaugh A J, Secor S M, Grosell M
Department of Marine Science, University of Texas at Austin, Marine Science Institute, 750 Channel View Drive, Port Aransas, TX 78418, USA.
Department of Biological Sciences, University of Alabama, Tuscaloosa, AL 35487-0344, USA.
Comp Biochem Physiol B Biochem Mol Biol. 2015 Sep;187:71-7. doi: 10.1016/j.cbpb.2015.05.006. Epub 2015 May 22.
Carbonic anhydrase (CA) is one of the most abundant proteins found in vertebrate erythrocytes with the majority of species expressing a low activity CA I and high activity CA II. However, several phylogenetic gaps remain in our understanding of the expansion of cytoplasmic CA in vertebrate erythrocytes. In particular, very little is known about isoforms from reptiles. The current study sought to characterize the erythrocyte isoforms from two squamate species, Python molurus and Nerodia rhombifer, which was combined with information from recent genome projects to address this important phylogenetic gap. Obtained sequences grouped closely with CA XIII in phylogenetic analyses. CA II mRNA transcripts were also found in erythrocytes, but found at less than half the levels of CA XIII. Structural analysis suggested similar biochemical activity as the respective mammalian isoforms, with CA XIII being a low activity isoform. Biochemical characterization verified that the majority of CA activity in the erythrocytes was due to a high activity CA II-like isoform; however, titration with copper supported the presence of two CA pools. The CA II-like pool accounted for 90 % of the total activity. To assess potential disparate roles of these isoforms a feeding stress was used to up-regulate CO2 excretion pathways. Significant up-regulation of CA II and the anion exchanger was observed; CA XIII was strongly down-regulated. While these results do not provide insight into the role of CA XIII in the erythrocytes, they do suggest that the presence of two isoforms is not simply a case of physiological redundancy.
碳酸酐酶（CA）是脊椎动物红细胞中含量最丰富的蛋白质之一，大多数物种表达低活性的CA I和高活性的CA II。然而，在我们对脊椎动物红细胞中细胞质CA扩展的理解上仍存在一些系统发育空白。特别是，关于爬行动物的同工型知之甚少。当前的研究旨在表征两种有鳞目物种（网纹蟒和菱斑水蛇）的红细胞同工型，并结合近期基因组计划的信息来填补这一重要的系统发育空白。在系统发育分析中，获得的序列与CA XIII密切聚类。在红细胞中也发现了CA II mRNA转录本，但其水平不到CA XIII的一半。结构分析表明，其生化活性与各自的哺乳动物同工型相似，CA XIII是一种低活性同工型。生化特性验证了红细胞中大部分CA活性归因于一种高活性的CA II样同工型；然而，用铜进行滴定支持存在两个CA池。CA II样池占总活性的90%。为了评估这些同工型的潜在不同作用，采用进食应激来上调二氧化碳排泄途径。观察到CA II和阴离子交换蛋白有显著上调；CA XIII则被强烈下调。虽然这些结果没有深入了解CA XIII在红细胞中的作用，但它们确实表明存在两种同工型并非仅仅是生理冗余的情况。
