Suberimidate crosslinking shows that a rod‐shaped, low cystine, high helix protein prepared by limited proteolysis of reduced wool has four protein chains

Structural Studies on the Microfibrillar Proteins of Wool: Characterization of the a-Helix-Rich Particle Produced by Chymotryptic Digestion

“…A similar degree of cross-linking was also attained with dimethyl adipimidate. The results are similar to those of Ahmadi and Speakman (1978) and lead to the conclusion that the helical particle has four polypeptide chains.…”

“…Speakman and collaborators (Campbell et al 1976;Lotay and Speakman 1977;Ahmadi and Speakman 1978;Ahmadi et al 1980) have prepared a highly IX-helical, rod-shaped particle, which they termed merokeratin AI, by limited tryptic digestion of reduced wool. From molecular weight studies in the ultracentrifuge and sodium dodecyl sulfate polyacrylamide gel electrophoresis they were unable to say whether there were three or four polypeptide chains in the particle.…”

Epidermal α-Keratin: Structure and Chemical Composition

“…However, during this period Ahmadi and Speakman (1978) suggested from cross-linking experiments on a wool fragment that in this tissue the oe-keratin filaments consist of four polypeptide chains arranged as two two-stranded coiled-coils. The significance of this in relation to epidermal oe-keratin was not immediately obvious, as the studies had been carried out on only a small proportion of the pro tein which was present in keratinized cells, i.e.…”

“…1 the filament could in fact have a "core" of lesser density compatible with the extensive data for a ring-co re structure and the essential difference between the two models would then be in the arrangement of subunits around the core. An advantage of the tetragonal arrangement is that, by requiring specific lateral aggregations of coiled-coils at a subtonofilament level it may more readily accommodate evidence such as that for the presence of overlapping dimers of three-stranded (Skerrow 1974;Steinert et al 1976) or two-stranded (Ahmadi and Speakman 1978;Woods and Gruen 1981;Gruen and Woods 1983) coiled-coils.…”

In vitro desmin assembly and in vivo changes in developing smooth muscle

“…More direct evidence from cross-linking studies has indicated, however, that protofilaments are composed of four subunits in the form of a pair of coiled-coils (Ahmadi and Speakman, 1978;Gruen and Woods, 1983;Woods and Inglis, 1984;). …”