Cha M K, Kim H K, Kim I H
Department of Biochemistry, Pai-Chai University, Taejon, Republic of Korea.
J Biol Chem. 1995 Dec 1;270(48):28635-41. doi: 10.1074/jbc.270.48.28635.
Three different molecular masses (24, 22, and 20 kDa) of antioxidant proteins were purified in Escherichia coli. These proteins exhibited the preventive effects against the inactivation of glutamine synthetase activity and the cleavage of DNA by a metal-catalyzed oxidation system capable of generating reactive oxygen species. Their antioxidant activities were supported by a thiol-reducing equivalent such as dithiothreitol. Analysis of the amino-terminal amino acid sequences and the immunoblots between 24- and 22-kDa proteins indicates that the 24-kDa protein is an intact form of the 22-kDa protein that was previously identified 22-kDa subunit (AhpC) of E. coli alkyl hydroperoxide reductase (AhpC/AhpF). We isolated and sequenced an E. coli genomic DNA fragment that encodes 20-kDa protein. Comparison of the deduced amino acid sequence of the 20-kDa protein with that of AhpC revealed no sequence homology. A search of a data bank showed that the 20-kDa protein is a new type of antioxidant enzyme. The synthesis of this novel 20-kDa protein was increased in response to oxygen stress during growth. The 20-kDa protein resides mainly in the periplasmic space of E. coli, whereas the 24-kDa AhpC resides mainly in the matrix. The 20-kDa protein was functionally linked to the thioredoxin as an in vivo thiol-regenerating system and exerted a peroxidase activity. This 20-kDa protein is thus named "thiol peroxidase," which could act as an antioxidant enzyme removing peroxides or H2O2 within the catalase- and peroxidase-deficient periplasmic space of E. coli.
在大肠杆菌中纯化出了三种不同分子量（24、22和20 kDa）的抗氧化蛋白。这些蛋白对谷氨酰胺合成酶活性的失活以及由能够产生活性氧的金属催化氧化系统导致的DNA裂解具有预防作用。它们的抗氧化活性由二硫苏糖醇等硫醇还原当量支持。对24 kDa和22 kDa蛋白的氨基末端氨基酸序列及免疫印迹分析表明，24 kDa蛋白是先前鉴定为大肠杆菌烷基过氧化氢还原酶（AhpC/AhpF）的22 kDa亚基（AhpC）的完整形式。我们分离并测序了编码20 kDa蛋白的大肠杆菌基因组DNA片段。将20 kDa蛋白推导的氨基酸序列与AhpC的序列进行比较，未发现序列同源性。数据库搜索显示，20 kDa蛋白是一种新型抗氧化酶。在生长过程中，这种新型20 kDa蛋白的合成会因氧应激而增加。20 kDa蛋白主要位于大肠杆菌的周质空间，而24 kDa的AhpC主要位于基质中。20 kDa蛋白在体内作为硫醇再生系统与硫氧还蛋白功能相关，并具有过氧化物酶活性。因此，这种20 kDa蛋白被命名为“硫醇过氧化物酶”，它可以作为一种抗氧化酶，在缺乏过氧化氢酶和过氧化物酶的大肠杆菌周质空间中清除过氧化物或H2O2。
