title: Comparison of purified human and rabbit serum paraoxonases.
abstract: Rabbit serum paraoxonase (PON) activity was reported to be nearly 20 times greater than that found for humans and all other mammalian species tested, to date. However, 85% of the amino acid residues are identical in human and rabbit PONs, and the two purified PONs show similar substrate specificity patterns. Both are stimulated by phospholipids and have two asparagine-linked sugar chains. Both also have one intramolecular disulfide bond and one free sulfhydryl residue per molecule. Both require Ca2+ for stability and for catalytic activity. Zn2+ and Cd2+ also stabilize both PONs and prevent irreversible denaturation, but neither metal confers catalytic activity. Maximum specific activities for both esterases were approximately 2,000 units of arylesterase activity/mg protein. In contrast, rabbit PON is more stable than human PON to heat inactivation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis treatment. Chelex 100 strips Ca2+ from human PON more easily, and EDTA is less inhibitory with rabbit PON. We conclude that human and rabbit PONs have very similar active centers, but the latter binds Ca2+ more tightly, is a more stable enzyme, and is maintained at 3- to 4-fold higher steady-state concentrations in serum than its human counterpart. PON activity depends on adequate Ca2+ being available; therefore, apparently much higher levels of PON activity in rabbits can be explained by the reduced Ca2+ concentrations present in the early assay methods.
authors.affiliation: Department of Environmental and Industrial Health, School of Public Health, University of Michigan Medical School, Ann Arbor 48109-0572, USA.
authors.forename: C L
authors.initials: CL
authors.lastname: Kuo
authors.forename: B N
authors.initials: BN
authors.lastname: La Du
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D043303:Aryldialkylphosphatase; D002614:Chelating Agents / Q000494:pharmacology; D004220:Disulfides / Q000737:chemistry; D004492:Edetic Acid / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D004950:Esterases / Q000037:antagonists & inhibitors / Q000097:blood* / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D010743:Phospholipids / Q000494:pharmacology; D011817:Rabbits; D012117:Resins, Synthetic; D013045:Species Specificity; D013268:Stimulation, Chemical; D013379:Substrate Specificity; D013438:Sulfhydryl Compounds / Q000737:chemistry
chemical_list: D002614:Chelating Agents; D004220:Disulfides; D010743:Phospholipids; D012117:Resins, Synthetic; D013438:Sulfhydryl Compounds; C024997:Chelex 100; D004492:Edetic Acid; D004950:Esterases; D043303:Aryldialkylphosphatase; D005947:Glucose