Distribution and some biochemical properties of rat paraoxonase activity.
The calcium-dependent enzyme activity which hydrolyzes the p-nitrophenyl-O-P bond of paraoxon (paraoxonase) has been studied in several rat and human tissues. Rat plasma and liver showed the highest activities (1.31 +/- 0.19, 0.82 +/- 0.09 nmol/min mg protein +/- SEM, respectively), while other tissues showed less than 2% plasma activity. The Arrhenius plot showed monophasic patterns in both tissues with activation energy values of Ea = 57 +/- 3 and 69 +/- 4 kcal/mol degree K for rat liver and plasma, respectively. Rat plasma and liver paraoxonase lost about 80% activity after 24-hr storage at 27-30 degrees C and was not restored by calcium addition. There was no loss of activity in human serum after 3 days and only 33% after 5 days. The pH optimum for paraoxonase activities was about 7.4 for both rat tissues. It is concluded that plasma paraoxonase is similar to the liver enzyme and is a good mirror for total body detoxifying activity.
Pellin
M C
MC
Departamento de Neuroquímica, Universidad de Alicante, Spain.
Moretto
A
A
Lotti
M
M
Vilanova
E
E
D000818:Animals; D043303:Aryldialkylphosphatase; D002151:Calorimetry; D004795:Enzyme Stability; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D009928:Organ Specificity; D010744:Phosphoric Monoester Hydrolases / Q000097:blood / Q000378:metabolism*; D051381:Rats
D010744:Phosphoric Monoester Hydrolases; D043303:Aryldialkylphosphatase