Regulation Of Actin-myosin Interaction Research Articles

Tropomyosin, in association with the troponin, is involved in the calcium-dependent regulation of act inmyosin interaction [ 1 ]. In skeletal muscles two major forms have been detected. In the rabbit, both of them possess 284 amino acid residues, 39 of which are different [2]. In spite of this similarity, their mobilities on SDS-polyacrylamide gels clearly differ. By convention, the faster migrating form is called c~-t ropomyosin, and the slower form 13-tropomyosin [3]. Minor forms have been described for c~and for /3-tropomyosin, differing in their primary sequences [2,4]. In cat [5] and chicken [6] skeletal nmscle, different c~-forlns associated with fast and slow skeletal muscle have been found. Furthermore, skeletal muscle tropomyosins can be phosphorylated, resulting in different electrophoretic mobilities [6]. It has been suggested that in mammals (and in particular in man), c~-tropomyosin is confined to type lI-fibers and ~3-tropomyosin to type I-fibers [7,8]. This contradicts the above-mentioned results from cat muscle [5]. Furthermore, in rabbit soleus muscle containing only few type lI fibers [9], both c~and 13-forms are present in roughly equal amounts [ 10]. Taking advantage of recently developed techniques for the analysis of the protein composition of typed single muscle fibers [ 11 ], we demonstrate in this study that in human skeletal muscle c~and 13-tropomyosins are present in about equal amounts in type I, IIA and IIB fibers. We also present evidence that the c~and H-forms display fiber type-specific characteristics. For this purpose, a new, two-dimensional peptide mapping

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