Paraoxonase phenotype distribution in Canadian Indian and Inuit populations

Solubilization and purification of A-esterase from mouse hepatic microsomes

A-esterase(s), an enzyme(s) that hydrolyzes certain organophosphate compounds, is located in mammals, primarily in serum and liver. Although considerable information is available regarding serum A-esterase(s), little is known about the hepatic form(s) of this enzyme. In the present study, hepatic A-esterase activity was quantified by measuring the EDTA-sensitive hydrolysis of the organophosphate paraoxon (O,O-diethyl-O-p-nitrophenyl phosphate). EDTA-insensitive hydrolysis was assumed to be the nonenzymatic phosphorylation of proteins with appropriate serine hydroxyl groups. Resuspension of mouse hepatic microsomes in 50 mM potassium phosphate buffer, pH 7.4, containing 100 microM calcium chloride, 0.25% sodium cholate, and 0.1% Triton N-101, resulted in the solubilization of A-esterase activity, as evidenced by the failure of activity to sediment after centrifugation at 100,000 g for 1 hr. Gel permeation chromatography followed by ion-exchange chromatography and nonspecific affinity chromatography resulted in a peak of A-esterase activity judged to be homogeneous by SDS-PAGE. A typical purification resulted in a 1531-fold increase in specific activity, with a recovery of 10%. SDS-PAGE with and without an acrylamide gradient indicated a molecular weight of 40,000 and 39,000 Da, respectively, while analyses of amino acid composition revealed similarities with human and rabbit serum paraoxonase. And finally, although this protein hydrolyzed both paraoxon and methyl paraoxon (O,O-dimethyl-O-p-nitrophenyl phosphate), it did not hydrolyze p-nitrophenyl acetate.

Interethnic differences in the detoxification of organophosphates: the human serum paraoxonase polymorphism

Paraoxon, 0,0-diethyl-0-p-nitrophenylphosphate is the highly toxic metabolite of parathion. The activity of paraoxonase, the enzyme which hydrolyses paraoxon in human serum shows a genetically influenced polymorphism with strong interethnic differences. The serum paraoxonase genotype has a significant influence on the paraoxon clearance and consequently on the toxic action of paraoxon and some related organophosphates and definitively protects the serum cholinesterase. Persons with low paraoxonase activity seem to be more endangered when handling parathion and related insecticides. More than 50% of all Europeans can be included in this group. The distribution of paraoxonase activity in human serum will be shown for samples which were collected from all over the world. As one moves from Europe in the direction of Africa and Asia the percentage of the low activity group decreases and was not even demonstrable in some tribes.

Ecogenetic studies in Atacameño Indians

Aldehyde dehydrogenase deficiency, N-acetyltransferase variation and the polymorphisms of alpha 1-antitrypsin, serum cholinesterase, paraoxonase, and delta-aminolevulinic acid dehydratase were investigated in 180 Atacameño Indians from the North of Chile. The genetic predisposition of these individuals for possible atypical reactions against environmental agents and drugs, as well as general implications of these findings, are discussed.