Esterase inhibition technique

Techniques. In 1962, McKinley and Read (42) developed an esterase-inhibition technique for the detection of organophosphate pesticide residues on paper chromatograms. The procedure involved conversion of the thiophosphates with bromine to yield active esterase inhibitors, the inhibition by the pesticide of the esterases from a beef liver homogenate sprayed onto the chromatogram, the hydrolysis of the substrate (a-naph-thyl acetate) which was sprayed onto the paper after the liver homogenate had dried, and the development of a background color between Fast Blue RR and the hydrolysis product, a-naphthol. 

Enzymatic techniques have also been employed in the analysis of these compounds. The toxicity of carbamate insecticides is due to the inhibition of the enzyme acetylcholine esterase, so the determination of these compounds can be achieved by enzyme inhibition (2,83,119), bioassay (118,167), or enzyme-linked immunosorbent assay (ELISA) (168-171). In the detection of carbamates by fluorimetric enzyme inhibition, the effluent from a reversed-phase chromatographic column was incubated with cholinesterase, which was introduced via a postcolumn reagent delivery pump. Then, the resulting partially inhibited cholinesterase was reacted with N-methyl indoyl acetate to produce a fluorophore and a reduction in the baseline fluorescence (172). 

The inhibition of carbonic anhydrase by anions has long been recognized. The inhibitory effect of Cl was noted by early investi-gators(19). A later study of anion inhibition by stopped-flow techniques was compromised by the presence of 80mM Cl in buffers used (20). The inhibition of the hydrase activity of the Cobalt(II) substituted enzyme has been investigated over the full pH range(21). Anionic inhibition of esterase activity has been studied by initial rate techniques(11-13) and by complexometric titration(22). None of the work thus far published has included full scale Michaelis-Menten analysis of the inhibition of the native Zinc(II) enzyme towards its natural substrate over an extended pH range. 

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