دانلود رایگان مقاله انگلیسی کاربرد آلکالین فسفاتاز تغییرپذیر H412R برای حذف فلزات سنگین از محلول تک یون و پساب - اشپرینگر 2018

Abstract

Enzyme-mediated bioremediation is an eco-friendly process for removing hazardous toxic heavy metals from the environment. The potential use of mutant alkaline phosphatase H412R for bioprecipitation of heavy metals such as Co2+, Cd2+, Cr6+, Ni2+, Mn2+ and Zn2+ from single-ion solutions and electroplating efuents was analysed in the present study. Purifed wild-type and H412R mutant alkaline phosphatase enzymes were incubated with an initial concentration of 100 ppm metal solutions for various time periods along with the substrate p-nitrophenol phosphate. Upon catalysis, the enzyme–substrate reaction liberates inorganic phosphate which in turn binds to heavy metals and precipitates them as metal-phosphates. The amount of metal ions precipitated as a result of formation of metal ion-phosphate complexes was determined by estimating the amount of free metal ions present in the solution using atomic absorption spectroscopy. Based on the results obtained, maximum bioprecipitation of metal ions, in general, was observed at 180 min of incubation period. The H412R mutant enzyme exhibited higher efciency and precipitated 96% of Mn2+ from electroplating efuent and 92% of Co2+ from the metal ion solution. The pattern of precipitation of various metal ions was in the order Co2+>Cr6+>Ni2+>Cd2+>Mn2+>Zn2+ for H412R mutant enzyme and Co2+>Cr6+>Zn2+>Ni2+>Cd2+>Mn2+ for wild-type enzyme. The results emphasise the use of novel H412R, a mutated alkaline phosphatase enzyme in its catalytic site, as an efcient way of achieving bioremediation of heavy metals from real-time efuents.

Conclusion

Of several physicochemical and biotechnological methods available, the use of enzymes immobilised in suitable matrices is gaining importance for bioremediation of heavy metals. The enzyme-mediated removal of toxic heavy metals is more convenient and much reliable since the time period required for the whole process is comparatively less and in addition, no toxic by-products are formed during the process. In the present study, ALP from P. aeruginosa was explored for the purpose and it was demonstrated that the enzyme subjected to site-directed mutagenesis for replacing histidine with arginine (H412R ALP) had resulted in signifcant improvement in the enzyme activity with a concomitant increase in the precipitation of various heavy metals such as cobalt, cadmium, chromium, nickel, manganese and zinc from single-ion test solutions as well as manganese and zinc from electroplating efuent. Quite signifcantly, the mutant enzyme could precipitate almost all manganese present in the electroplating efuent. Thus, it appears that there is ample scope for further research on creating mutations at the active site to achieve a higher turnover number for the enzyme for facilitating more precipitation of metals even with lesser amount of the recombinant enzyme, perhaps in an immobilised state.