Binding of mercury compounds to the chloroplasts in relation to the inhibition of the Hill reaction |
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Authors: | SS Lee RD Wauchope Rizwanul Haque SC Fang |
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Institution: | Department of Agricultural Chemistry, Oregon State University, Corvallis, Oregon 97331 USA |
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Abstract: | The binding behavior of mercuric chloride (HgCl2), phenylmercuric acetate (PMA), and ethylmercuric chloride (EMC) to the spinach chloroplasts in relation to the inhibition of the Hill reaction was studied at pH 6.8 and 7.8 using 203Hg labeled compounds. The pH of the reaction medium did not influence the amount of mercury binding of the chloroplast at various mercurial concentrations, but it altered the inhibition curve of the Hill reaction. Between 0–1 × 10?5M the binding of Hg2+ and EMC were similar and increased linearly with the concentration, while the binding of PMA was similar to the binding of Hg2+ only at a concentration below 4 × 10?6M and was less when the concentration was above 4 × 10?6M. However, the inhibition of the Hill reaction by these mercury compounds was quite different; at pH 7.8, the I50 values for Hg2+, PMA, and EMC were 5 × 10?6, 2.5 × 10?6, and 2.5 × 10?6M, respectively, while at pH 6.8, these values were 4 × 10?6, 4 × 10?5, and 2 × 10?4M, respectively. The differential block of electron flow by the mercury compounds at pH 6.8 and 7.8 was further confirmed by electron spin resonance study. |
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