APOLIPOPROTEIN-J IS ASSOCIATED WITH PARAOXONASE IN HUMAN PLASMA

Apolipoprotein J (apoJ)-containing high-density lipoproteins (HDL), is olated from human plasma by immunoaffinity chromatography, are associa ted with apoAI and a protein of approximately 44 kDa. In order to adva nce our understanding of apoJ's role in the vasculature, a comprehensi ve investigation was performed to identify and characterize this 44-kD a protein and to study its interaction with apoJ. The 44-kDa protein, a monomeric glycoyslated polypeptide, was identified by N-terminal seq uencing as serum paraoxonase. Paraoxonase exists in two oxidation stat es: one contains all free cysteines while the other has one disulfide bond between Cys42 and Cys284. Northern analysis of eight human tissue s shows paraoxonase message present only in the liver. The majority of apoJ/paraoxonase-HDL are 90-140 kDa; however, not all of the plasma p araoxonase is associated with apoJ. The specificity-of the apoJ/paraox onase interaction, inferred by the constant mole ratio of the two prot eins in affinity-purified apoJ-HDL, is confirmed in direct binding ass ays. For purified proteins, there is more than a 5-fold increase in th e apparent affinity of apoJ for immobilized paraoxonase as the paraoxo nase coating concentration is increased from 0.5 to 2.0 mug/mL. Both o xidation states of paraoxonase bind to apoJ with equal affinity. Our d ata combined with other evidence suggest that the plasma link of apoJ with paraoxonase will be implicated as a predictor of vascular damage.