Circadian rhythms of hepatic molybdenum hydroxylases activities in the rat

Abstract EN

The objectives of this study is to investigate the occurrence of circadian rhythms with molybdenum hydroxylases as many other enzymes were found to show this phenomenon.

The specific activities of molybdenum hydroxylases, namely; aldehyde oxidase and xanthine oxidase were measured in partially purified ammonium sulfate fractions of adult rat liver eight times daily at equal intervals.

The activity of aldehyde oxidase was found to vary markedly with the substrates used (3-methylisoquinoline and phthalazine).

The highest enzyme activity with both substrates was observed at 1500 hr, whereas the lowest activity occurred at 0900 hr.

There were highly statistically significant (P < 0.0005) differences between the maximum and minimum activities.

Circadian variation was also observed in xanthine oxidase activity when xanthine was used as a substrate.

Two main maximum peaks appeared at 1500 hr and 2100 hr, and the minimum activity peak was shown at 0300 hr.

The difference between the rhythmic extremes was statistically significant (P < 0.0005).

These results indicate that some factors such as hormones, may be responsible for the circadian variations exhibited in aldehyde oxidase and xanthine oxidase activities.