X-ray studies of muscle

Abstract

No X-ray diffraction photographs have yet been obtained of muscle in the very act of contracting or relaxing, but much work has been carried out in the approaches to this goal. I reviewed the situation in 1945 in my Croonian Lecture (Astbury 1947 a ), and the present contribution may serve partly to recall some of the main conclusions already arrived at then, but chiefly to develop them in relation to more recent discoveries. In all the kinds of muscles that have so far been examined by X-rays the dominating feature has been found to be the fibrous protein myosin lying along the direction of the myofibrils; further structural components have been revealed according to the type of muscle, it is true, but myosin at least seems to be essential, and there are very strong reasons, not only from X-rays but from much other evidence besides, for believing that it is indeed the mainspring of the contractile apparatus proper. Many X-ray and accessory studies have been carried out on it both in situ and after extraction, and it is a principal inference from such investiga­tions that, whatever the detailed steps by which contraction and recovery are contrived in muscle itself, myosin has at any rate properties peculiarly fitted for these purposes. The myosin molecule or complex is inherently elastic; it can be caused to change its internal configuration and thereby alter its length over a large range.