Can phase response curves of various treatments of circadian rhythms be explained by effects on protein synthesis and degradation?
The phase response curves of circadian rhythms toward pulses of various chemical and physical perturbations are standardized and compared in Gonyaulax, Phaseolus, Kalanchoe, Trifolium, and Aplysia. The time of maximal phase shift, in many of these curves clustered around a given time of day, especially in Gonyaulax and Aplysia. This could be interpreted as being due to a converging effect of these modalities on a single function that is decisive for the mechanism of the circadian clock. Since many of the treatments that results in significant phase response curves (e.g., light pulses, hormones, temperature pulses, changes of ion concentration, etc) have also been shown in independent studies to be capable of affecting protein synthesis, it is possible that these treatments may all affect circadian rhythmicity by virtue of their direct or indirect effect on protein synthesis. There is also a number of treatments which give phase response curves that are not clustered, especially in Phaseolus. This means either that our original assumption is incorrect or that these treatments impinge on sensitive compounds of the clock other than protein synthesis. It is emphasized, however, that the phasing of the phase response curve on one hand is subject to variability of the boundary conditions of the different laboratories and on the other hand seems to depend on the strength, direction, and modality of the perturbing pulse.