The kinetics of phytochrome transformation were examined over a 30°C temperature range (+5° to–25°C) in 75% glycerol. Two new intermediate reaction stages are described for the transformation of the red‐absorbing form, Pr to the far‐red absorbing form, Pfr The free energies, enthalpies and entropies of activation were obtained for five of the six reaction stages observed in the transformation of Pr to Pfr and for the two reaction stages observed in the reverse process. All exhibited positive entropies of activation with the maximum being 25 entropy units. The results suggest that the phototransformations between Pr and Pfr consist of relaxation processes beginning with the intermediate produced immediately upon absorption of a quantum of light and ending with either Pr or Pfr.
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Pratt et al. (1970) studied this question.
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