THE X-ray diffraction photographs usually obtained from apparently nonfibrous proteins have so much in common with one another and with the photographs given by certain natural protein fibres when disoriented that the inference seems clear that all proteins at some stage of their existence are fibrous in the molecular sense [Astbury, 1933; 1934,1,2]. Recently [Astbury and Lomax, 1934, 1, 2;1935] this concept has been expressed as a generalised interpretation of denaturation in the conclusion that the two more stable and insoluble states of protein structure, the fibrous and the denatured, are based on fundamentally similar modes of molecular arrangement; that, in fact, the denatured state2 is essentially a fibrous state inasmuch as it always consists of peptide chains, often fully extended, and aggregated after coagulation in parallel bundles, as in fibroin [Meyer and Mark, 1928], f3-keratin [Astbury and Street, 1931; Astbury and Woods, 1933], /3-myosin [Astbury and Dickinson, 1935], fibrin [Katz and De Rooy, 1933] etc. Itwas found that heat-denaturation of the albumins, for instance, merely makes the X-ray photograph more like that of a random arrangement of fibres of/-keratin (stretched hair, horn, etc.; cf. Plate V, Figs. 1 and 3). ,B-Keratin is built from almost fully-extended polypeptide chains linked side-to-side, firstly by combinations between their side-chains ("side-chain linkage "), and secondly in a direction at right angles [Astbury and Sisson, 1935], through attractions between the =CO and =NH groups of neighbouring main-chains ("backbone linkage"). The three-dimensional structure is that of a pile of polypeptide "grids ", the average distance apart of the main-chains in the plane of each grid being about 9*8 A. ("side-chain spacing") and the distance between the grids being 4*65 A. (" backbone spacing "). These two spacings correspond respectively to the two reflections, 001 and 200, seen on the equator of Fig. 4: they are the two prin'cipal side-spacings of the ,B-keratin crystallites, whilst the reflection 020 (spacing about 3*4 A.) gives the average length of an amino-acid residue in the direction of the main-chains. Fig. 4 is a "fibre photograph" of crystallites all pointing roughly in the same direction (the fibre-axis) and taken with the X-ray beam perpendicular to this direction; but when the crystallites are 1 Beit Scientific Research Fellow. 2 The seed globulins, at least, appear to pass through an intermediate fibrous state before reaching complete denaturation. It is possibly better therefore to reserve the word "denatured"

IT has been shown both for the case of isolated frog's muscle and for certain human muscular movements (1,3,4) that the work done in a maximal contraction is diminished hy increase of rate of shortening. The relation between the work done and the speed of shortening is found to be linear, so that the relation between the work W and the time t occupied by the contraction is given by the equationwhere WO and k are constants. WO represents the theoretical maximum work and would be attained only if the contraction could take place infinitely slowly. k represents the theoretical minimum time and would be attained only if no external work were done. From experiments on isolated frog's muscle a relation has been found between the theoretical maximum work WO, the energy H liberated in an isometric contraction excited by a maximal stimulus, and the time t during which the stimulus lasts. It is given by the equationwhere a and b are constants: a represents the energy required to set up a contraction capable of doing one unit of work under maximal conditions: the product ab represents the energy required per second of stimulus to maintain that contraction. From equations (1) and (2) it can be deduced (5) that the mechanical efficiency E of a muscular movement will be given by the equation I -(k/t) E (i ....t) (3).

No abstract

[P lates [15][16][17] The X -ra y an d elastic properties of m yosin are found to resem ble m ost closely, n o t those of n a tu ra l k eratin , b u t those of k e ra tin th a t has suffered breakdow n am ong th e cross-linkages (including disulphide bridges) of th e polypeptide grid. The su p erco n tractio n of m yosin cannot be explained as due sim ply to d isorientation of long th in u n its : it m u st involve a fu rth er folding of th e polypeptide chain system . The fact th a t m yosin an d k eratin are sim ilar in b o th m olecular configuration an d elastic properties is discussed in th e light of recent X -ra y an d chem ical findings, and th e X -ray in terp retatio n is given of th e d e n a tu ra tio n of m yosin. I n t r o d u c t o r yX-ray studies of the molecular structure and properties of animal hairs (Astbury and Street 1931; Astbury and Woods 1933; Astbury and Sisson 1935 ' Woods 1938)* lead naturally to comparable studies of muscle tissue, if only because both types of structure are protein and fibrous, but par ticularly because both show similar long-range elastic phenomena and give similar X-ray photographs (Astbury 1933a(Astbury , 1934. Previous X-ray studies of muscle (Herzog and Jancke

Some of the deformed single crystals (10, 12 and 16 per cent extension) have again become single crystals after recrystallisation at temperatures coinciding with those of Karnopp and SacJ.1s1, but with an orientation absolutely different from that of the deformed crystal (see Fig. 1, c and d).N. SELJAKOW. Institute of Metals, E. Sows. Leningrad.