 chromium is an environmentally significant human carcinogen with complicated metabolism and an unknown mechanism of mutagenesis . 
 chromium(vi ) is taken up by cells as the chromate anion and is reduced intracellularly via reactive intermediates to stable cr(iii ) species . 
 chromium(iii ) forms tight complexes with biological ligands , such as dna and proteins , which are slow to exchange . in vitro 
 , crcl3.6h2o primarily interacts with dna to form outer shell charge complexes with the dna phosphates . 
 however , at micromolar concentrations , the cr(iii ) binds to a low number of saturable tight binding sites on single - stranded m13 dna . 
 additional chromium interacts in a nonspecific manner with the dna and can form intermolecular dna cross - links . 
 although high concentrations of cr(iii ) inhibit dna replication , micromolar concentrations of cr(iii ) can substitute for mg2 + , weakly activate the klenow fragment of e. coli dna polymerase i ( pol i - kf ) , and act as an enhancer of nucleotide incorporation . 
 alterations in enzyme kinetics induced by cr(iii ) increase dna polymerase processivity and the rate of polymerase bypass of dna lesions . 
 this results in an increased rate of spontaneous mutagenesis during dna replication both in vitro and in vivo . 
 our results indicate that chromium(iii ) may contribute to chromate - induced mutagenesis and may be a factor in the initiation of chromium carcinogenesis.imagesfigure 1 . 
Images