Ecotoxicological Effects Of Terbium On Horseradish Peroxidase

The extensive application of rare earths in the China agriculture has been brought remarkable economic benefits. However, environmental security of rare earths is concerned tremendously by Chinese and foreign scientists. In this paper, using measures of plant physiology, biochemistry and chemicobiology, the influence of terbium(Tb) on some physiological indexes in horseradish were discussed, ecotoxicological effects of Tb on horseradish were studied. A new peroxidase-containing Tb complex (Tb-HRP) was obtained from horseradish after treatment with Tb. Then, the enzymatic molecule structure and character of HRP and Tb-HRP were investigated. It can provide the experiment gist for heavy rare earth ecotoxicological theory to the protective enzyme, and scientific evaluation for economic harm and environmental risk. The main results obtained are as follows:(1) The effects of Tb on the physiological indexes of horseradish was shown dose-effect and time-effect relationship. The physiological indexes of horseradish could be improved by the low concentration of Tb in short period, increasing the contents of chlorophyll, soluble protein and HRP activity, decreasing membrane permeability and MDA content, compared with controls, while presented toxic effects in long period. Under the high Tb concentration, the toxic effects were significantly.(2) Compared with other physiological indexes, HRP was the most sensitive to Tb stress, HRP was more significantly to Tb stress. what's more, a new peroxidase was induced under Tb stress(3) A new peroxidase was obtained from horseradish after treatment with Tb, which contained the Tb element. Compared with HRP, metal cations contents in each molecule of Tb-HRP complex, was one calcium, one iron and three terbium, molecular weight was 43650Da.(4) Compared with HRP, Tb-HRP was sensitive to changes of pH value and temperature. when apart from optimum value of pH value and temperature, Tb-HRP activity significantly decreased. The affinity to substrates of guaiacol and H2O2 was lower than HRP, as well as reactive capacity. Further more,Tb-HRP the electrochemical reaction and catalytic activity was inhibited.(5) Tb could bind to N or O atoms of amide in the amino groups in the peptide chain of HRP and replace one calcium by forming the Tb-HRP complex. The conformation of protein was changed, leading to the increase in the planarity of the porphyrin cycle in the heme group, and then the decrease in the extent of exposure of the electrochemically active center-Fe in the porphyrin cycle of the heme groupin Tb-HRP molecule, and Fe spin state was changed, hence inhibiting the bioactivity of Tb-HRP.