HUMAN AND RABBIT PARAOXONASES - PURIFICATION, CLONING, SEQUENCING, MAPPING AND ROLE OF POLYMORPHISM IN ORGANOPHOSPHATE DETOXIFICATION

Human and rabbit paraoxonases/arylesterases were.purified to homogenei ty by chromatographic and gel electrophoretic/isofocusing procedures c oupled with activity stains. N-terminal and peptide sequence analysis suggested retention of the secretion signal sequence and allowed desig n of oligonucleotide probes. The probes were used to isolate a 1294-bp rabbit paraoxonase cDNA clone, which, in turn, was used to isolate th ree human cDNA clones. Comparison of rabbit and human protein and cDNA sequences indicated a high degree of sequence conservation (approxima tely 85% identity) and verified that paraoxonase retains its signal se quence (except for the N-terminal Met). The rabbit cDNA encodes a prot ein of 359 amino acids and the human a protein of 355 amino acids. In situ hybridization demonstrated, as expected, that the paraoxonase gen e maps to the long arm of human chromosome 7. Arginine at position 192 specifies high activity paraoxonase and glutamine low activity human paraoxonase. Variation in protein levels explains the variation of enz yme activity observed within a genetic class. Toxicity studies showed that raising rat plasma paraoxonase levels by i.v. administration of p artially purified rabbit paraoxonase protected animals against choline sterase inhibition by paraoxon and chlorpyrifos oxon. Protection corre lated with the relative rates of hydrolysis of these two compounds.