ACTIVATION OF PARATHION BY LIVER OF HYPOSTOMUS-PUNCTATUS, A BRAZILIAN BENTHIC FISH (CASCUDO)

1. Organophosphorus activation ability of Hypostomus punctatus liver was demonstrated by an in vitro metabolization curve of parathion into paroxon. 2. A calibration curve of paroxon acetylcholinesterase inhibition indicated that about 6.0% of parathion was biotransformed after 2 hr of incubation when the medium contained 0. 5 mg of parathion per litre and 0. 1 5 mg of protein. 3. Identification of incubation products by thin layer and gas chromatography showed that paroxon was not the unique resulting product. 4. Microsomal liver activation of parathion was largely dependent on reduction by NADH or NADPH but was only partially inhibited by SKF-525A and CO.