Determination of Organophosphorus Acid Anhydrase in Blood

In an attempt to develop a new conceptual approach to paraoxon antagonism by encapsulating organophosphorus acid anhydrase (OPA anhydrase) into carrier erythrocytes, it necessitated the spectral determination of OPA anhydrase activity in blood. OPA anhydrase determination usually is conducted in serum or plasma. This presents a problem, because blood contains various substances that interfere with the determination of OPA anhydrase. This enzyme used paraoxon as the substrate, liberating p-nitrophenol and diethylphosphate. OPA anhydrase has a broad substrate specificity and is capable of hydrolyzing other organophosphorus compounds, i.e., pesticides, nerve gases, etc. Blood OPA anhydrase activity was determined with paraoxon as the substrate. This reaction was terminated by adding hydrochloric acid to the reaction mixture. The p-nitrophenol then was extracted with dichloromethane, and p-nitrophenol was determined at 400 nm. The sensitivity of this method can be greatly enhanced by increasing the sample siz...