Open AccessOptical Spectroscopic Study of the ADP‐Myosin Interaction
Author(s) -
MARSH David J.,
d'ALBIS Anne,
GRATZER Walter
Publication year - 1978
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1978.tb12014.x
Subject(s) - heavy meromyosin , chemistry , myosin , fluorescence , circular dichroism , adenosine diphosphate , binding site , pyrophosphate , biophysics , crystallography , stereochemistry , biochemistry , enzyme , biology , platelet aggregation , physics , platelet , quantum mechanics , immunology
The binding of ADP to heavy meromyosin, and the separated subfragment 1 components S‐1 (A1) and S‐1 (A2), has been observed by ultraviolet spectrophotometry. The results are compatible with the presence of spectroscopically equivalent and independent sites, one per head, at both 10°C and 25°C. We do not observe the heterogeneity of binding and of the spectroscopic response that has been reported. The binding has also been followed by other methods sensitive to the effect of ligand on the aromatic residues of the protein, viz. intrinsic fluorescence of heavy meromyosin and changes in the near‐ultraviolet Cotton effects of myosin, and its active fragment. Within the limits of our experimental precision, the binding profiles, based on concentration of myosin heads, are the same for myosin as for subfragment 1. A perturbation in the circular dichroism is also generated by pyrophosphate, which compets with ADP. The spectra suggest that subsites for the purine ring and the diphosphate can be recognised. The sensitivity of binding profiles obtained by methods of the kind used here to cooperative or antagonistic interactions between the binding sites has been analysed. It is clear that sizeable effects of this nature could be concealed by the binding curves, even for high experimental precision.