Measurement of neurotoxic esterase activity in various subcellular fractions of hen brain and sciatic nerve homogenates and the effect of diisopropyl fluorophosphate (DFP) administration

Abstract

Both the membrane and soluble compartments of brain and nerve tissue contain esterase activity. Experiments were done to assess neurotoxic esterase (NTE) activity in different subcellular fractions, obtained from brain and sciatic nerve homogenates. The inhibitory effect of diisopropyl fluorophosphate (DFP) on the various subcellular fractions was also studied. High levels of neurotoxic esterase activity was associated with the microsomal fractions (100,000 g pellet) from brain and sciatic nerve extracts. All other subcellular fractions from brain homogenates yielded lower NTE activity. The comparative study of brain versus sciatic NTE activity demonstrated that substrate hydrolysis by sciatic microsomal fractions was much less than obtained with brain microsomes. The results showed that the percentage NTE of the total paraoxon-resistant activity was lower in sciatic nerve microsomal preparations than in brain microsomal fractions. Brain cytosol fractions (100,000 g supernate) contained lower NTE activity than the corresponding sciatic nerve cytosol fraction. Myelin fractions were devoid of neurotoxic esterase activity. DFP had an overall inhibitory effect on microsomal and cytosol NTE activity. Based on the association of NTE with the microsomal fraction, neurotoxic esterase can be classified as a β-esterase. The results also indicate that quantitative differences exist both in the activity and in the quantity of NTE of the total paraoxon-resistant esterases of CNS and PNS.