A butyrylcholinesterase in the early development of the brine shrimp ( Artemia salina) larvae: a target for phthalate ester embryotoxicity?

The phthalate ester insensitive blue-green algae ( Synechococcus lividus) were used as a food source to extend the survival of synchronously hatched brine shrimp ( Artemia salina) larvae allowing measurement of a reduced toxic response to phthalate esters at late post-hatching stages of development. The maximum acute toxicity due to di- n-butyl phthalate (DNBP) correlated with the expression of a phthalate ester-hydrolyzing enzyme. The purified enzyme was identified as a butyrylcholinesterase due to its rapid inactivation by low concentrations (10 −7 M) of diisopropyl fluorophosphate and inhibition by physostigmine (IC 50=6×10 −7 M) and tetraisopropylpyrophosphoramide (I-OMPA, IC 50=5×10 −6 M) but not by BW284c5. Apparently competition of the phthalates with the endogenous substrates of the enzyme led to development-dependent toxicity.