Natural Variability in the Length of Thin and Thick Filaments in Single Fibres From a Crab, Portunus Depurator
TL;DR: It can be deduced that passive length changes occur in crab fibres by sliding of thin and thick filaments by means of a possible model of the filament.
Abstract: The carpopodite flexor of the walking legs of the crab Portunus depurator contains fibres belonging to 3 groups. These are characterized by differences in the cross-striation spacing. Fibres having sarcomeres of approximately 4, 5 and 7 µm are here called short, medium and long sarcomere types, respectively. Within individual fibres belonging to any of the groups the length of the A band is not constant. Up to 25 % length differences have been measured in A bands belonging even to the same fibril. The bridge-free regions of the thick filaments are not always in the centre, so that the filaments are often asymmetric. Analogally, the L line, resulting from the alignment of the bridge-free regions of the thick filaments, may be asymmetrically placed in the Z band. The length of the bridge-free region in crab thick filaments is 60 nm, while the corresponding region in vertebrate thick filaments is 120 nm. This is discussed in terms of a possible model of the filament. The length of the thin filaments is proportional to that of the thick filaments in the corresponding portion of the sarcomere. When two A bands of different length occur in adjacent positions along the fibril, the Z line is not a centre of symmetry. The ratio of thin to thick filament number is variable in individual fibrils. In general, the ratio is higher in the medium sarcomere type fibres than in the short sarcomere type. Stretched and shorter portions of single fibres of the medium type have been examined and the A-band length populations compared. From such a study it can be deduced that passive length changes occur in crab fibres by sliding of thin and thick filaments.
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TL;DR: The structure and function of the major regulatory proteins, troponin and tropomyosin, and also the main cytoskeletal protein, connectin (titin), are described, and new aspects of protein chemistry might be revealed from work on such a giant peptide as connectin.
Abstract: Publisher Summary This chapter describes the structure and function of the major regulatory proteins, troponin and tropomyosin, and also of the main cytoskeletal protein, connectin (titin). The effective contractile machinery of vertebrate striated muscle represents an elaborate framework. The motion of myosin and actin filaments is controlled by regulatory proteins and their position is supported by cytoskeletal proteins. Approximately 65% of the total myofibrillar proteins are myosin and actin, the contractile proteins of muscle. There are a number of both regulatory and cyotoskeletal proteins. The troponin and tropomyosin are the best characterized proteins, together with actin and myosin, in the field of muscle biochemistry. They are involved in the Ca2+ regulation of muscle contraction. On the other hand, connectin—an elastic protein—is a relative newcomer, and because of its huge molecular weight (more than 2 million), its physicochemical characterization has remained incomplete. Nevertheless, it may be appropriate to call attention to this protein, because new aspects of protein chemistry might be revealed from work on such a giant peptide as connectin.
222 citations
TL;DR: The effects of lattice change on muscle contraction in vertebrate skeletal and cardiac muscle and in invertebrate striated muscle are reviewed and the force developed, the speed of shortening, and stiffness are compared with structural changes occurring within the lattice.
Abstract: Millman, Barry M. The Filament Lattice of Striated Muscle. Physiol. Rev. 78: 359–391, 1998. — The filament lattice of striated muscle is an overlapping hexagonal array of thick and thin filaments w...
219 citations
TL;DR: Intermediate high voltage stereo electron microscopy of rabbit portal-anterior mesenteric vein smooth muscle showed that thick filaments are 2·2 μm long and have tapered ends, which could contribute to the ability of smooth muscle to develop equal or greater tension than striated muscle.
195 citations
TL;DR: This chapter presents data to indicate that the assembly of the free thick and thin myofilaments, into the double hexagonal array, can proceed in the absence of protein synthesis and may be another example of a self-assembly system.
Abstract: Publisher Summary This chapter reviews the recent electron microscopic and biochemical studies relevant to an understanding of the construction of myofibrils in striated muscle. Emphasis is placed on relating ultrastructural information to data obtained from the in vitro studies of the myofibrillar proteins and their respective myofilaments. It focuses primarily on vertebrate myofibrillogenesis, but as the problem is common to the development of all striated muscle, much of the discussion is relevant to both invertebrate and vertebrate species. It limits an analysis of the posttranslational steps in fibrillogenesis and the ultrastructural features of myogenic cells. The structure and chemistry of the organelle is reviewed briefly. The chapter presents data to indicate that the assembly of the free thick and thin myofilaments, into the double hexagonal array, can proceed in the absence of protein synthesis and may be another example of a self-assembly system. The distribution of polyribosomes in myogenic cells has been reviewed and it was concluded that no consistent morphological relationship exists between the polysome chains and the growing myofilaments. The close relationship of myofibrillogenesis to the inner surface of the plasma membrane has been noted and discussed at some length.
174 citations