PT  - JOURNAL ARTICLE
AU  - C L Kuo
AU  - B N La Du
TI  - Comparison of purified human and rabbit serum paraoxonases.
DP  - 1995 Sep 01
TA  - Drug Metabolism and Disposition
PG  - 935--944
VI  - 23
IP  - 9
4099  - http://dmd.aspetjournals.org/content/23/9/935.short
4100  - http://dmd.aspetjournals.org/content/23/9/935.full
SO  - Drug Metab Dispos1995 Sep 01; 23
AB  - 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.