Kusano T, Ji G Y, Inoue C, Silver S
Department of Microbiology and Immunology, University of Illinois College of Medicine, Chicago 60680.
J Bacteriol. 1990 May;172(5):2688-92. doi: 10.1128/jb.172.5.2688-2692.1990.
Mercuric reductase activity determined by the Thiobacillus ferrooxidans merA gene (cloned and expressed constitutively in Escherichia coli) was measured by volatilization of 203Hg2+. (The absence of a merR regulatory gene in the cloned Thiobacillus mer determinant provides a basis for the constitutive synthesis of this system.) In the absence of the Thiobacillus merC transport gene, the mercury volatilization activity was cryptic and was not seen with whole cells but only with sonication-disrupted cells. The Thiobacillus merC transport function was compared with transport via the merT-merP system of plasmid pDU1358. Both systems, cloned and expressed in E. coli, governed enhanced uptake of 203Hg2+ in a temperature- and concentration-dependent fashion. Uptake via MerT-MerP was greater and conferred greater hypersensitivity to Hg2+ than did uptake with MerC. Mercury uptake was inhibited by N-ethylmaleimide but not by EDTA. Ag+ salts inhibited mercury uptake by the MerT-MerP system but did not inhibit uptake via MerC. Radioactive mercury accumulated by the MerT-MerP and by the MerC systems was exchangeable with nonradioactive Hg2+.
通过氧化亚铁硫杆菌merA基因（在大肠杆菌中克隆并组成型表达）测定的汞还原酶活性，是通过203Hg2+的挥发来测量的。（克隆的硫杆菌汞决定簇中不存在merR调控基因，这为该系统的组成型合成提供了基础。）在缺乏硫杆菌merC转运基因的情况下，汞挥发活性是隐蔽的，完整细胞中看不到这种活性，只有超声破碎的细胞中才能看到。将硫杆菌merC转运功能与质粒pDU1358的merT-merP系统的转运功能进行了比较。这两种系统在大肠杆菌中克隆并表达后，均以温度和浓度依赖的方式控制203Hg2+的摄取增强。与MerC摄取相比，通过MerT-MerP的摄取量更大，对Hg2+的超敏感性也更高。汞摄取受到N-乙基马来酰胺的抑制，但不受EDTA的抑制。银盐抑制MerT-MerP系统的汞摄取，但不抑制通过MerC的摄取。MerT-MerP和MerC系统积累的放射性汞可与非放射性Hg2+交换。
