Abstract

Camel is continually exposed to stressful desert environment that enhances generation of reactive oxygen species, including hydrogen peroxide (H₂O₂). Catalase plays an important role in detoxification of H₂O₂. A highly active catalase from camel kidney was purified to homogeneity, with a specific activity of 1,774,392 U/mg protein, using ion exchange and metal chelate affinity chromatography. The molecular weight of the enzyme was 268 kDa consisting of four identical subunits of 63 kDa. The enzyme showed higher optimum temperature (45 °C) and higher activation energy (4.37 kJ mol⁻¹). The thermodynamic parameters, ΔH, ΔG and ΔS, were determined. The effect of various metal ions and chemicals on enzyme activity was investigated. K_m, V_max, k_cat and k_cat/K_m values for H₂O₂ were found to be 46 mM, 10,715,045 U/mg, 48,265,968 s⁻¹ and 2,966,562 s⁻¹mM⁻¹, respectively. Camel kidney catalase displayed higher affinity efficiency for H₂O₂ and can protect reduced glutathione (GSH) from oxidation by H₂O₂. Sodium azide was found to be a noncompetitive inhibitor of enzyme with K_i and IC₅₀ of 17.88 µM and 20.94 µM, respectively. Camel catalase showed unique biochemical properties. Interestingly, camel catalase can protect molecules (GSH) and organ functions (kidney) from the toxic effects of H₂O₂ induced by stressful desert environment.

摘要

骆驼持续暴露在充满压力的沙漠环境中，这会增加活性氧的产生，包括过氧化氢 (H ₂ O ₂ )。_{过氧化氢酶在H 2} O ₂的解毒中起重要作用。使用离子交换和金属螯合物亲和层析，将来自骆驼肾的高活性过氧化氢酶纯化至均质，比活性为 1,774,392 U/mg 蛋白质。该酶的分子量为 268 kDa，由四个相同的 63 kDa 亚基组成。该酶表现出较高的最适温度（45 °C）和较高的活化能（4.37 kJ mol ⁻¹）。确定了热力学参数ΔH、ΔG和ΔS。研究了各种金属离子和化学物质对酶活性的影响。发现H ₂ O _2的K _m、V _max、k _cat和k _cat / K _m^{值分别为46 mM、10,715,045 U/mg、48,265,968 s -1}和2,966,562 s ^-1 mM ^-1。骆驼肾过氧化氢酶对 H ₂ O ₂表现出更高的亲和效率，并且可以保护还原型谷胱甘肽 (GSH) 免受 H ₂ O _2氧化。叠氮化钠被发现是一种非竞争性酶抑制剂，K _i和 IC ₅₀分别为 17.88 µM 和 20.94 µM。骆驼过氧化氢酶表现出独特的生化特性。有趣的是，骆驼过氧化氢酶可以保护分子（GSH）和器官功能（肾脏）免受应激沙漠环境引起的H ₂ O ₂的毒性作用。