Bony fish muscles

Luther et al. (1996) conducted a systematic study of the occurrence of the simple lattice and superlattice across the vertebrate kingdom. Superlattices are present in the muscles of all the higher vertebrates, namely, in mammals (including humans), in amphibians, in birds, in reptiles, and in some muscles of cartilaginous fish. Simple lattices occur in all the teleost (bony fish) muscles so far studied, in some muscles of cartilaginous fish, and also in some primitive fish such as sturgeons and bowfin. 

A typical low-angle diffraction pattern from relaxed bony fish muscle is shown in Fig. 4B. Much of the intensity that is seen comes from the organization of the myosin heads on the myosin filaments in the resting state (probably mainly MADP.Pi). We know that the myosin heads lie approximately on three co-axial helices of subunit translation 143 A and repeat 429 A. This is most easily represented by the radial net shown in Fig. 16B-D. The radial net in D is like an opened-out surface view of the filament in B. Here the helical tracks become straight lines, and the black blobs represent the origins on the myosin filament surface of the pairs of myosin heads in each myosin molecule. From early studies it is known that the three crowns within the 429 A repeat are not exactly the same and that there is a perturbation. 

Figure 19A shows a field of negatively stained isolated myosin filaments from bony fish muscle, together with actin filaments in the background. 

Harford, J. J., and Squire, J. M. (1986). The crystalline myosin crossbridge array in relaxed bony fish muscles. Biophys. J. 50, 145-155. 

This armory affords consideration of the diffraction from the components of the muscle sarcomere. Note first that muscles are not single crystals of the kind illustrated in Fig. 3A. The sarcomeres themselves can have varying degrees of order some, like insect flight muscle and bony fish muscle, are almost crystalline within an A-band or sarcomere. But, whatever the muscle, both different myofibrils within a fiber, and different... 

Fig. 12. (A) The left half of a low-angle diffraction pattern from bony fish muscle...

Fig. 13. Illustrations of the possible arrangement of C-protein (MyBP-C) on the myosin filament backbone in projection down the axis (A) and in axial view (B). Of particular importance here is the possibility that the N-terminal half of C-protein extends out and binds to actin in relaxed muscle. (C) Simulation of the possible interactions of C-protein with binding sites on actin generated using the program MusLABEL (Squire and Knupp, 2004). (D) Left left half of the low-angle X-ray diffraction pattern from bony fish muscle (as in Fig. 11C), showing (right) the possible positions where the C-protein array in (D) might contribute. (From Squire elal, 2003d.)...

Fig. 14. Model of the A-band filament lattice in bony fish muscle, based on Hudson et al. (1997) and Squire et al. (2003d), showing the central myosin filament with its projecting myosin heads, together with C-protein in orange and actin filaments colored as in Fig. 11A and B.

Fig. 15. Intensity profiles along the equator of the bony fish muscle low angle X-ray diffraction pattern from muscles at rest (A), fully active (B), and in rigor (C). The indexing in (A) is based on the hexagonal A-band lattice, and the arrows indicate peaks that come from the Z-band. (C) to (F) are computed electron density maps based on the amplitudes of the A-band peaks in (A) to (A), respectively. The simple lattice unit cell is outlined in (D). (From Harford and Squire, 1997.)...

Fig. 19. Tension, intensity, and spacing time courses from the rising phase of tetanic contractions in bony fish muscle (from Mok et al., 2005). All changes have been normalized to be 0% in resting muscle and 100% at the tetanus plateau for all changes that are increases, and vice versa for all changes that are decreases. (A) Shows the changes of the tension (T), the Al and A2 actin layer lines, and the All (11) equatorial reflection. (B) Shows the M3 spacing and intensity relative to tension (T). (C) Shows the changes of the myosin layer line ML3 and of ML1 at the All and A20 positions. For details, see text.

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