Trong chương này, các cơ chế đề kháng với các ion kẽm kim loại nặng, cadmium, chì, đồng, thạch tín, và antimon ở vi khuẩn sẽ được mô tả. Ngoài ra, các con đường kháng chất hóa học trong prokaryote Saccharomyces cerevisiae sẽ được thảo luận. Mặc dù thường được nhóm lại như kim loại nặng, các ion của các kim loại này tốt hơn mô tả như là các ion kim loại mềm, mà là những người có quyền lực phân cực cao (một tỷ lệ lớn phí ion với bán kính của ion), trái ngược với các ion. | 15 Microbial Resistance Mechanisms for Heavy Metals and Metalloids Mallika Ghosh and Barry P. Rosen Wayne State University School of Medicine Detroit Michigan 1. INTRODUCTION In this chapter the mechanisms of resistance to ions of the heavy metals zinc cadmium lead copper arsenic and antimony in bacteria will be described. In addition the pathways of arsenical resistance in the prokaryote Saccharomyces cerevisiae will be discussed. Although often grouped as heavy metals the ions of these metals are better characterized as soft metal ions which are those with high polarizing power a large ratio of ionic charge to the radius of the ion in contrast to the hard metal ions of Groups I and II such as Na and Ca2 . This distinction between hard and soft metals is important biologically. When considering how these metals interact with biological molecules such as proteins hard metals most frequently bind to proteins weakly through ionic interactions with functional groups such as carboxylates of glutamate or aspartate residues. In contrast soft metals form much stronger nearly covalent bonds with functional groups such as the thiolates of cysteine residues and the imidazolium nitrogens of histidine residues. These strong interactions with proteins account for much of the biological toxicity of soft metals. All of these ions are toxic in excess and bacterial metal resistances probably arose early in evolution owing to widespread geochemical sources of metals. Copyright 2002 Marcel Dekker Inc. Resistance genes to inorganic salts of soft metals including arsenic antimony lead cadmium copper nickel zinc bismuth and mercury are found both on extrachromosomal plasmids and in chromosomes of bacteria archaea and eukaryotes. For metals such as copper and zinc which are required in low amounts but toxic in high amounts the efflux systems are components of the homeostatic mechanisms that maintain intracellular concentrations at optimal levels. Recent reviews have been written on .
