Abstract
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 °K for rat liver and plasma, respectively. Rat plasma and liver paraoxonase lost about 80% activity after 24-hr storage at 27–30°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.
Published Version
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