| Abstract: | Hydrodynamic calculations lead to the conclusion that chymotryptic (or ethylenediaminetetraacetic acid) myosin S1 in solution (hydrated), at 1-5 degrees C, can be modeled as a prolate ellipsoid, with an axial ratio lying between p = 1.0 and 2.5 (major axis between 100.5 A, for p = 1.0, and 162.5 A, for p = 2.5). The degree of hydration is considerable (1.24 g/g for p = 2.5 and 2.02 g/g for p = 1.0). The dehydrated myosin head is pear-shaped under the electron microscope, and its narrowest part is located near the junction with the tail Elliott, A., & Offer, G. (1978) J. Mol. Biol. 123, 505-519]. Mendelson & Kretzschmar Mendelson, R. A., & Kretzschmar, K.M. (1980) Biochemistry 19, 4103-4108] have shown that the pear-shaped molecule does not predict the experimental X-ray scattering curve. Nor is this model able to predict the hydrodynamic values. The three-dimensional model for S1 used by Mendelson and Kretzschmar gives a rather good fit to the experimental X-ray scattering curve, but it does not predict the hydrodynamic values. In order to try to reconcile the three models and to fit the X-ray scattering curve and the hydrodynamic data, we suggest that, in solution, the S1 monomer has the shape of a prolate ellipsoid and that an inclusion of bound water exists at one extremity of the protein. The rest of bound water surrounds the protein. As first approximation, the dry protein and the hole are assumed to have the same shape as the hydrated molecule (prolate ellipsoid; p).(ABSTRACT TRUNCATED AT 250 WORDS) |
