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Photoreversible association of phytochrome with membranes. II. Reciprocity tests and a model for the binding reaction
Author(s) -
NAPIER R. M.,
SMITH H.
Publication year - 1987
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/1365-3040.ep11603633
Subject(s) - phytochrome , cooperative binding , membrane , biophysics , binding site , cooperativity , phytochrome a , divalent , chemistry , dimer , allosteric regulation , reciprocity (cultural anthropology) , biology , biochemistry , receptor , botany , arabidopsis thaliana , red light , social psychology , psychology , organic chemistry , gene , mutant
Abstract A series of fluence‐response curves for the binding of phytochrome to membranes in the absence of divalent cations, as described by Watson & Smith (1982), were constructed to demonstrate that the response obeys the law of reciprocity. Analysis of the binding of P fr (the far‐red‐absorbing form of phytochrome) showed that two P fr molecules bind to the membrane for each P r (the form with an absorption maximum in the red) photoconverted to P fr in the intrinsic membrane‐bound phytochrome pool. Using this stoichiometry we have been able to model the binding curve of Pr and match the binding data. P r binding can be simulated if P r binds only as a consequence of the binding of P fr , i.e. when P fr is part of a P r : P fr dimer. The enrichment of the membranes with P fr as a result of the binding of P fr was also accurately simulated. There is no binding cooperativity. Phytochrome binding is a low‐fluence response and the possibility that it has physiological significance as a mediator of phytochrome action is discussed.