DAMPED SINUSOIDAL OSCILLATIONS OF CYTOPLASMIC REDUCED PYRIDINE NUCLEOTIDE IN YEAST CELLS

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Abstract
The rapid reduction and re-oxidation of cytoplasmic pyridine nucleotide observed upon addition of glucose or in the aerobic-anaerobic transition of baker''s yeast studied over the past dozen years now appears to be the initial phase of a damped train of sinusoidal oscillations. Provided appropriate levels of glycolytic intermediates are present, the oscillations may be started when the mitochondrial control of the ADP and phosphate levels ceases because of inhibition of respiration. The oscillations are evaluated quantitatively on the basis of engineering criteria for a pulsed-sinusoidal oscillator, and show damping factors as low as 1.1 and Q values as high as 8. The oscillation frequency is 1.7 min-1 at 26[degree] and 4.0 min-1 at 35[degree]. The oscillations which were observed as fluctuations in the DPNH concentration in the cytoplasm are a consequence of variations of the glyceraldehyde-3-phosphate-dehydrogenase activity in conjunction with other dehydrogenases of the cytoplasm. A possibility of generating continuous oscillations in this system and their relevance to biological clocks are discussed.