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Temperature effects upon the time course of contraction and reextension in Stentor coeruleus
Author(s) -
Nielsen Lis Engdahl,
Rotne Jens
Publication year - 1985
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1041240123
Subject(s) - contraction (grammar) , kinetics , chemistry , thermodynamics , reaction rate constant , biophysics , biology , physics , endocrinology , quantum mechanics
A double‐flash microphotographic technique has been used to follow the variation with temperature of the following kinetic parameters related to the contraction and reextension of the ciliate Stentor coeruleus , namely the rate of contraction, the initiation time before contraction, the rate of reextension and the initiation time before reextension, all described by first order kinetics. Activation enthalpies, entropies and free energies related to the above mentioned parameters were calculated from the variation of the rate constants with temperature. The enthalpies and entropies appear to be of minor interest compared to the free energies. For the contraction and the initiation of contraction the ΔG‡ values obtained were 14 and 15 kcal/mole, respectively, while the reextension and the initiation of reextension both were represented by a value of ΔG‡ about 19 kcal/mole. These results are compared to activation parameters for different motile systems and for the formation and breakdown of ATP‐myosin complexes. A model for the contraction and reextension processes is proposed in accordance with the results measured.