Characterization of proteases in the hamster suprachiasmatic nucleus

The activities of several proteases in the hamster suprachiasmatic nuclei were measured at different time points throughout the daily or circadian cycle. No variation for metalloproteinase A (MMP-2) activity was found, while metalloproteinase B (MMP-9) was rhythmic and maximally active during the night. In addition, diurnal variations for two low molecular weight proteases were determined, with peaks during the light phase. This rhythmicity appears to be under exogenous control, since constant darkness abolished fluctuations throughout the circadian cycle. These results suggest that protein degradation in the hamster circadian clock is regulated in a diurnal fashion.