The toxic effects of lead(II) have been studied in Escherichia coli cells. Using microcalorimetric analysis, it was shown that E. coli growth was inhibited in the presence of Pb2+ resulting from damage to the cell membrane and that Pb2+ takes part in the metabolism of cells. Treatment with lysozyme confirms damage to the cell's outer membrane. Similarities between the ionic radii and charge/radius ratio cause Pb(II) to replace Ca(II) at the binding sites of lipopolysacharides, leading to rupture of protecting areas on the cell's surface. Consequently, the protection and functionality of outer membrane is lost, thus becoming the basis for the biological effect of Pb2+ on E. coli.
The nonspecific interaction between lead ions and bovine serum albumin (BSA) was studied by the calorimetric technique. According to thermodynamic parameters calculated from titration curves, it can be seen that the increase of intermolecular bond energies and decrease of disorder in the system were accompanied by a binding process. This kind of binding is the reaction "driven by enthalpy." Furthermore, the denatured BSA has more binding sites and more changes in enthalpy and entropy than the native BSA because the unfolded chain of denatured BSA could adapt itself to the binding reaction with lead ions more easily.
The toxic mechanism of La3+ to Escherichia coli is investigated by detecting the concentration change of La3+ in E. coli cells growing in La3+-containing medium. Stimulatory action and inhibitory effect of La3+ in different concentrations can be attributed to the permeability alteration of the cell. Low concentration of La3+ increases the nutrition absorbability of the cells from the cultures as a result of increased cell permeability, and high concentration of La3+ causes the accumulation of La3+ in cells, resulting in the toxic effects on the E. coli cells.
By means of microcalorimetry, the effect of four copper(II) complexes on Tetrahymena growth was investigated. The extent and duration of the inhibitory effect on the metabolism, judged by the rate constant, k, and the half inhibition concentration, IC(50), varied with the different complexes. The results showed that the half inhibition concentrations IC(50) of CuCl(2), (C(9)H(6)NO)(2)Cu and [Cu(phen)(2)]Cl(2)[Symbol: see text]6H(2)O were 9.9 x 10(-4), 2.0 x 10(-4), and 2.6 x 10(-4) mol/L, respectively. The sequence of antibiotic activity of these three complexes was: (C(9)H(6)NO)(2)Cu > [Cu(phen)(2)]Cl(2)[Symbol: see text]6H(2)O > CuCl(2). The growth rate constants of [Cu(phen)(3)]Cl(2)[Symbol: see text]6H(2)O did not change obviously with the increase of concentrations, but [Cu(phen)(3)]Cl(2)[Symbol: see text]6H(2)O also can prolong the time of Tetrahymena growth.
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