Daily Rhythmic Variations of Renal Molybdenum Hydroxylases in Male Rats

The activities of the xenobiotic metabolizing enzymes, aldehyde oxidase and xanthine oxidase were estimated eight times daily (at equal periods) in partially purified preparations of kidney of rats. diurnal variation in aldehyde oxidase activity was observed with two substrates (phthalazine and 3-methylisoquinoline). the maximum peak appeared at 0300h whereas the minimum activity occurred at 15h. the differences between the maximum and minimum enzyme activities were extremely significant (p < 0.0005). xanthine oxidase also showed a daily rhythm when xanthine was used as a substrate. the maximum of activity xanthine oxidase occurred at 0300 h whereas the minimum occurred at 1500h. from a statistical point of view, the difference between rhythmic extremes was significant (p < 0.0005).