An X-ray and electron microscope study of tropomyosin

Tropomyosin: a new asymmetric protein component of the muscle fibril

“…3-3 when Iu = 0-1, c = 0.815%) are still high in comparison with 274 I948 those of 'corpuscular' proteins. This high viscosity, even in salt solutions, first suggested that the molecule was inherently asymmetric, a conclusion fully supported by diffusion studies (Bailey et al 1948), X-ray studies (Astbury et al 1948), and by the high values obtained for the intrinsic viscosity. Again, the large increase in viscosity occurring after removal of salt appeared too large to explain except in terms of a polymerization into relatively large fibres, which were later seen in the electron microscope (Astbury et al 1948).…”

“…This high viscosity, even in salt solutions, first suggested that the molecule was inherently asymmetric, a conclusion fully supported by diffusion studies (Bailey et al 1948), X-ray studies (Astbury et al 1948), and by the high values obtained for the intrinsic viscosity. Again, the large increase in viscosity occurring after removal of salt appeared too large to explain except in terms of a polymerization into relatively large fibres, which were later seen in the electron microscope (Astbury et al 1948). This property was difficult to explain until the completion of the aminoacid analysis, when it became clear that it was related, partly at least, to the high complement of dissociating groups Which tend greatly to enhance the interaction of the protein with salt and of one protein molecule with another.…”

“…Whilst the emphasis in considering th.e function both of adenosine triphosphatase and of actin has been upon their possible role in the contractile process, the properties of this newer component suggest that it is a prototype of the much larger myosin molecule and might conceivably be a unit utilized in the elaboration of myosin itself. The evidence for this view derives partly from a consideration of its physical properties and amino-acid composition, but more particularly from its relation to the keratinepidermis-myosin-fibrinogen (k-e-m-f) group as revealed by X-ray and electron optical studies, reported by Astbury, Reed & Spark (1948) in an accompanying paper. The protein has been designated tropomyo8in, not so much to describe its function, which as yet is.…”

The packing of α-helices: simple coiled-coils

“…Although the fibrous ~-proteins all give the ~-keratin pattern in the loose sense, they give it to varying degrees of perfection, African porcupine quill having sharp spots (McArthur, 1943) whereas films of tropomyosin (Astbury, Reed & Spark, 1948) give only a diffuse pattern. The more diffuse the ~-keratin pattern becomes, the more it resembles a very diffuse pattern from a synthetic polypeptide, that is, a diffuse ~-helix pattern.…”

“…The equatorial reflexions near 10 J~ would be expected to be rather diffuse and perhaps at a rather greater average spacing than usual, owing to the difficulties of packing. This is a fair description of the X-ray results of Astbury, Reed & Spark (1948) for stretched films of tropomyosin. These films also give a 1-5 ~ meridional reflexion (Astbury, reported by Perutz, 1952), as one would predict.…”