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Effect of Various Heavy Metals on the Enzymatic Activity of E. Coli Alkaline Phosphatase


Affiliations
1 Departments of Chemistry, U.A.E. University, Al-Ain, P.O. Box: 17551, United Arab Emirates
     

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Bacterial alkaline phosphatase (ALP) is essential for efficient recycling of phosphorous in the soil. However, soil pollution by various heavy metals has the potential to affect soil microbial ALP activity and adversely affect soil quality. To assess the effect of various heavy metal pollutants on E. coli ALP, we carried out a systematic study to examine the effect of Cd<SUP>2+</SUP>, Hg<SUP>2+</SUP>, Cu<SUP>2+</SUP>, Co<SUP>2+</SUP>, Ca<SUP>2+</SUP> (individually as well in combination) on ALP activity. Additionally, we tested the effect of UV radiation and hydrogen peroxide on E. coli ALP in the presence or absence of these heavy metals. Our results show that Hg<SUP>2+</SUP>, Cu<SUP>2+</SUP>, and Cd<SUP>2+</SUP> all readily inhibited E. coli ALP (Hg2+ and Cu2+ were most inhibitory, followed by Cd<SUP>2+</SUP>). However, Co<SUP>2+</SUP> had minor activating effect on ALP. Furthermore, as expected, divalent alkaline earth metals like Ca<SUP>2+</SUP> and Mg<SUP>2+</SUP> activated the enzyme. Incubation of H2O2 alone also caused significant reduction of ALP activity, which was further enhanced when combined with heavy metals. UV radiation which alone had very little effect of ALP activity, dramatically enhanced the inhibitory effects of the heavy metals tested. Co-incubation studies suggest a cumulative inhibitory effect when Cu<SUP>2+</SUP> and Hg<SUP>2+</SUP> were incubated together with ALP. Interestingly, incubation of Ca<SUP>2+</SUP> decreases the inhibitory effect of Cd<SUP>2+</SUP>, however, no such protection was observed when Ca2+ was incubated with Hg2+. In summary our results show that heavy metal pollutants can readily inhibit E. coli ALP with some of them being additive in their inhibition. Also, we show that oxyradical generating conditions (UV radiation or H2O2) can further dramatically increase the adverse affects of heavy metals on E. coli ALP.

Keywords

Alkaline Phosphatase, Heavy Metals, Pollution, UV Radiation, H2O2, Oxyradicals, Oxidative Stress
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  • Effect of Various Heavy Metals on the Enzymatic Activity of E. Coli Alkaline Phosphatase

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Authors

Maitha M. Alnuaimi
Departments of Chemistry, U.A.E. University, Al-Ain, P.O. Box: 17551, United Arab Emirates
Ibtesam A. Saeed
Departments of Chemistry, U.A.E. University, Al-Ain, P.O. Box: 17551, United Arab Emirates
S. Salman Ashraf
Departments of Chemistry, U.A.E. University, Al-Ain, P.O. Box: 17551, United Arab Emirates

Abstract


Bacterial alkaline phosphatase (ALP) is essential for efficient recycling of phosphorous in the soil. However, soil pollution by various heavy metals has the potential to affect soil microbial ALP activity and adversely affect soil quality. To assess the effect of various heavy metal pollutants on E. coli ALP, we carried out a systematic study to examine the effect of Cd<SUP>2+</SUP>, Hg<SUP>2+</SUP>, Cu<SUP>2+</SUP>, Co<SUP>2+</SUP>, Ca<SUP>2+</SUP> (individually as well in combination) on ALP activity. Additionally, we tested the effect of UV radiation and hydrogen peroxide on E. coli ALP in the presence or absence of these heavy metals. Our results show that Hg<SUP>2+</SUP>, Cu<SUP>2+</SUP>, and Cd<SUP>2+</SUP> all readily inhibited E. coli ALP (Hg2+ and Cu2+ were most inhibitory, followed by Cd<SUP>2+</SUP>). However, Co<SUP>2+</SUP> had minor activating effect on ALP. Furthermore, as expected, divalent alkaline earth metals like Ca<SUP>2+</SUP> and Mg<SUP>2+</SUP> activated the enzyme. Incubation of H2O2 alone also caused significant reduction of ALP activity, which was further enhanced when combined with heavy metals. UV radiation which alone had very little effect of ALP activity, dramatically enhanced the inhibitory effects of the heavy metals tested. Co-incubation studies suggest a cumulative inhibitory effect when Cu<SUP>2+</SUP> and Hg<SUP>2+</SUP> were incubated together with ALP. Interestingly, incubation of Ca<SUP>2+</SUP> decreases the inhibitory effect of Cd<SUP>2+</SUP>, however, no such protection was observed when Ca2+ was incubated with Hg2+. In summary our results show that heavy metal pollutants can readily inhibit E. coli ALP with some of them being additive in their inhibition. Also, we show that oxyradical generating conditions (UV radiation or H2O2) can further dramatically increase the adverse affects of heavy metals on E. coli ALP.

Keywords


Alkaline Phosphatase, Heavy Metals, Pollution, UV Radiation, H2O2, Oxyradicals, Oxidative Stress

References