Data Analysis and Processing in X-ray Diffraction Studies of Scattering From Myosin Heads in Muscle

Abstract

The X-ray diffraction pattern of muscle tissue contains sharp reflections from ordered structures, and a region of diffuse scatter from disordered structures. The sharp reflections have been studied in detail over many years, but the diffuse scatter has received much less attention, apart from the pioneering work of J. Lowy and F. R. Poulsen, reviewed in the book 'Fibrous Protein Structure' edited by J. Squire and P. Vibert (Academic Press, 1987). In this thesis a set of FORTRAN programs were written to analyse diffraction data, with particular emphasis on the diffuse scatter. Film patterns from some synchrotron experiments and from some of J. Lowy and F. R. Poulsen’s archived material were analysed, to study the effects of varying osmolarity and/or sarcomere length on the sharp reflections and the diffuse scatter. Conclusions were drawn about the feasibility of using the diffuse scatter as an indication of changes in myosin subfragment 1 (the head of the myosin molecule), and of retrieving scattering data from the archived material which had been taken largely to observe sharp reflections. It was concluded that although the archived material could give interesting indications about physiological effects, new experiments were needed to confirm these indications, and these new experiments should be designed specifically towards the diffuse scattering data. In the course of this work, I have considered the possibility of using Guinier plots to derive information on head shapes from data on intact muscle, and the precision with which such information can be obtained. I conclude that the Guinier plots do contain information about the myosin heads in intact muscle, but that the accuracy of the information may not be much better than ±10%, and this may not be sufficient to confirm or deny possible conformation changes in the myosin head. However, I do not consider that the work done in this thesis reached the limit of accuracy, and further experiments may be worthwhile.