ULTRADIAN RHYTHMICITY OF TYROSINE AMINOTRANSFERASE ACTIVITY IN EUGLENA-GRACILIS - ANALYSIS BY COSINE AND NONSINUSOIDAL FITTING PROCEDURES

Although the geophysical periodicity of the earth's rotation corresponds to a biological cyclicity of ca. 24 h, cellular temporal organization comprises a multifrequency time structure, in which ultradian rhythms may be regarded as subelements of the circadian oscillator. In Euglena gracilis kept under conditons in which various cellular functions oscillate with a circadian period, tyrosine aminotransferase activity exhibited predominantly an ultradian cycle, whereas its circadian frequency was only weakly expressed. Ultradian period lengths were in the range of 4-5 h, as demonstrated by least squares fitting of cosines and of a non-sinusoidal regression function. © 1990 International Society of Biometeorology.