Action of organophosphorus compounds on the cation-sensitive p-nitrophenyl phosphatase of membranes from the retinal nerve of the squid

The cation-sensitive p-nitrophenyl phosphatase of nerve membranes is inhibited by DFP and the non-phosphorylating analogue triisopropyl phosphate. The inhibition requires 5–20 mM concentrations and is partly irreversible. The inhibition is distinct from that produced by the non-ionic detergent lubrol. Under some conditions dithiothreitol can inhibit the enzyme activity; under other conditions it can protect it against inactivation. The extent of the inactivation by DFP and triisopropyl phosphate is reduced in the presence of dithiothreitol. It is suggested that the primary action of the organophosphorus compounds is to change the reactivity of membrane sulphydryl or disulphide groups. The relevance of these findings to the blocking of conduction in the axon are discussed.