An ultra-sensitive enzyme imhibitory method for the detection of mercury ion using a novel thiol amylase from the plant

Abstract

A simple method is essentially required for routine analysis of Hg2+ in drinking water, assuring highest limit of 1 ppb in the same. We reported earlier the purification of a 43 KDa thiol amylase (containing 3 SH groups/ mole) from Tinospora cordifolia, capable of completely hydrolyzing both starch and amylopectin, without the formation of limit dextrin. We now report an analytical method based on the inhibition of thiol amylase activity by Hg2+, monitored by starch-iodine color. Hg2+ showed an irreversible non-competitive inhibition with Ki = Ki’ = 3.5 + 0.25 nM and IC50 value of 1.9 + 0.25 ppb. The method is much more sensitive than other enzymatic methods (thiol urease, bromelain, papain, trypsin) used for detection of Hg2+. The method could detect Hg2+ at a minimum concentration of 0.5 ppb. The method was insensitive to the presence of (50 ppm) other heavy metals like Pb2+, Cd2+, and Cu2+ . The method remained insensitive upto 400 ppm of Ca2+.