Phospholipids in myofibrils

The myofibrils were shown to be lipoprotein structures. Lipoprotein nature of these structures was confirmed by their lipid phosphorus to protein ratio in a completely dispersed myofibril preparation of the skeletal muscle cells. The ratio was found to be 49.65 ± 3.95 microgram P / mg protein. The phospholipids present in the myofibril preparation were determined to be phosphatidylcholine and phosphatidylethanolamine.     

Structure of the cross-striated adductor muscle of the scallop

The structure of the cross-striated adductor muscle of the scallop has been studied by electron microscopy and X-ray diffraction using living relaxed, glycerol-extracted (rigor), fixed and dried muscles. The thick filaments are arranged in a hexagonal lattice whose size varies with sarcomere length so as to maintain a constant lattice volume. In the overlap region there are approximately 12 thin filaments about each thick filament and these are arranged in a partially disordered lattice similar to that found in other invertebrate muscles, giving a thin-to-thick filament ratio in this region of 6:1.The thin filaments, which contain actin and tropomyosin, are about 1 μm long and the actin subunits are arranged on a helix of pitch 2 × 38.5 nm. The thick filaments, which contain myosin and paramyosin, are about 1.76 μm long and have a backbone diameter of about 21 nm. We propose that these filaments have a core of paramyosin about 6 nm in diameter, around which the myosin molecules pack. In living relaxed muscle, the projecting myosin heads are symmetrically arranged. The data are consistent with a six-stranded helix, each strand having a pitch of 290 nm. The projections along the strands each correspond to the heads of one or two myosin molecules and occur at alternating intervals of 13 and 16 nm. In rigor muscle these projections move away from the backbone and attach to the thin filaments.In both living and dried muscle, alternate planes of thick filaments are staggered longitudinally relative to each other by about 7.2 nm. This gives rise to a body-centred orthorhombic lattice with a unit cell twice the volume of the basic filament lattice.     

Enzymes in thick filaments of vertebrate cross-striated muscles]

Contemporary data on three enzymes of vertebrate cross-striated muscle thick filaments, such as creatine kinase, AMP-deaminase and phosphofructokinase, are reviewed. The physico-chemical, enzymatic and regulatory properties and localization of these enzymes in different zones of the thick filament are considered. The functional relevance of localization of creatine kinase, AMP-deaminase and phosphofructokinase on thick filaments is discussed in terms of the possible role of the enzyme adsorption on subcellular structures in regulation of metabolic processes.     

Extracellular cross-striated banded structures in human connective tissue.

Extracellular cross-striated banded structures have been found in the connective tissues of a variety of organs. Rarely have they been found in conditions such as: hyperplastic parathyroid, follicular adenoma of the thyroid, metastatic hemangiopericytoma in the lung, sarcoidosis of lymph node, and two biopsies of nerve as reported here. The shape and size of the structure varies, as well as its periodicity, which is usually in the range of 1000 to 15000 A. An unusual exception to this general rule is the banded structure in the follicular adenoma of the thyroid where the periodicity is 270 A. These structures are quite different from native collagen or experimentally reconstituted long-space collagen, both by staining reaction with phosphotungstic acid or uranyl acetate and lead nitrate, and in their ultrastructural morphology.     

Identification of troponin-I of crayfish myofibrils

Crayfish (Procambarus clarkii) myofibrils contain two basic proteins of molecular weights of 25,000 and 23,000. Both of the two proteins inhibit actomyosin ATPase as the vertebrate troponin-I does. These results differ from the previous one that troponin-I of crayfish (Astacus leptodactylus) showed a single band on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE).