title: Methods for measuring serum activity levels of the 192 Q and R isoenzymes of paraoxonase 1 in QR heterozygous individuals.
abstract: BACKGROUND
  Paraoxonase 1 (PON1), an esterase that hydrolyzes toxic organophosphates and has antioxidative and antiatherogenic properties, contains a common polymorphism at position 192: glutamine (Q) or arginine (R). The Q and R isoenzymes exhibit different physical and protective properties. We describe 2 methods for quantifying their serum activity levels.
  
  
  METHODS
  We measured serum hydrolytic activity with paraoxon [paraoxonase (PXN) activity], phenylacetate [arylesterase (AE) activity], and diazoxon [diazoxonase (DZN) activity] with standard automated assays. We determined PON1 Q192R genotypes with PCR and Q192R phenotypes using the PXN/AE and PXN/DZN ratios. Interpolation equations were empirically derived to predict the percentage of total PON1 hydrolytic activity due to the Q isoenzyme (%Q) from the PXN/AE and PXN/DZN ratios; %R is 100 - %Q. We estimated Q and R isoenzyme activity levels in sera from 2095 veterans by multiplying AE activity, a measure of total PON1 hydrolytic activity, by %Q and %R.
  
  
  RESULTS
  In all 2095 samples, the PXN/AE and PXN/DZN ratios predicted Q192R phenotypes with nearly identical accuracy (κ = 0.997). In the 925 QR heterozygotes, the 2 interpolation methods predicted Q and R isoenzyme activity levels with excellent agreement (intraclass correlation 0.94). After excluding a few genotype/phenotype-discordant samples, the percentage of total PON1 activity due to the Q isoenzyme ranged from 22% to 70%.
  
  
  CONCLUSIONS
  These new interpolation methods allow accurate estimation of PON1 192 Q and R isoenzyme activity levels, increasing specificity and power for studying susceptibility to disease.
authors.affiliation: Department of Internal Medicine, Division of Epidemiology, The University of Texas Southwestern Medical Center, Dallas, TX 75390-8874, USA. john.teiber@utsouthwestern.edu
authors.forename: John F
authors.initials: JF
authors.lastname: Teiber
authors.forename: Gerald L
authors.initials: GL
authors.lastname: Kramer
authors.forename: Robert W
authors.initials: RW
authors.lastname: Haley
mesh_terms: D000328:Adult; D000368:Aged; D043303:Aryldialkylphosphatase / Q000097:blood* / Q000235:genetics; D005260:Female; D006579:Heterozygote; D006801:Humans; D006868:Hydrolysis; D007527:Isoenzymes / Q000097:blood / Q000235:genetics; D008297:Male; D008875:Middle Aged; D010641:Phenotype
chemical_list: D007527:Isoenzymes; D043303:Aryldialkylphosphatase; C468406:PON1 protein, human