Rigor state

Figure 9. A schematic representation of crossbridge orientation assumed from electron micrographs of insect flight muscle in relaxed and rigor states by Reedy et al. (1965). The crossbridge is thought to have an orientation of 90° to the thick filament axis in the relaxed state and an orientation of 45° to the thick filament axis in rigor.

Ando, T. (1984) Fluorescence of fluorescein attached to myosin SHI distinguishes the rigor state from the actin-myosin-nucleotide state. Biochemistry 23, 375. 

How We Become a Stiff When a higher vertebrate dies, its muscles stiffen as they are deprived of ATP, a state called rigor mortis. Explain the molecular basis of the rigor state. 

Multi dimensional quantum mechanical calculations are needed for the quantitative description of the effects discussed above. Rigorously stated, such calculations are very laborious. In this connection, considerable attention has been paid during the last two decades to the development of simplified methods for resolving the multi-dimensional problems. We refer, for instance, to the method of classic S-matrix [60] and the quantum-mechanical method of the transition state [61]. The advantage of these methods is the use of realistic potential energy surfaces the shortcoming is the fact that only... 

Fig. 31. Implications about the contractile mechanism in insect flight muscle. Blue is insect flight muscle SI shape in pre-powerstroke state (Al-Khayat et al., 2003), and green is chicken skeletal muscle SI in the rigor state with no nucleotide bound (Rayment et al., 1993a). The actin filament (right) is shown with the Z-band at the bottom and M-band at the top. A transition from the pre-powerstroke/resting SI shape to the rigor/end of post-powerstroke shape would involve an axial swing of the lever arm by 100 A, resulting in the sliding of the actin filaments past the myosin filaments and toward the M-band.

D. Rigor State Actin Binding Closes the 50K Cleft. 171... 

Fig. 3. Details of the seven-stranded /1-sheet and associated structures (A and B) in the post-rigor conformation and (C and D) in the pre-powerstroke conformation. The orientation of A and C is at right angles to that shown in Fig. 2. When attached to actin, it corresponds to that shown in Fig. 5B. The colors are as in Fig. 2. The views shown in B and D are at right angles to A and C looking out radially from the axis of the actin helix. Note the kink in the relay helix shown in C and D that leads to a 60° rotation of the converter domain. This in turn rotates the lever arm 60°. The P-loop (which constitutes the ATP-binding site) and the adjoining a-helix are shown in yellow. The flanking switch sequences (1 and 2) are also shown. The strands of the /1-sheet are numbered from the N-terminal (distal) end of the sheet. The lower part of strand 5 (light blue) constitutes switch 2. In the post-rigor state, switch 2 lies out of the plane of the /1-sheet (open) and in the pre-powerstroke state switch 2 is in the plane of the /1-sheet (closed).

The strongly bound pre-powerstroke state or top-of-powerstroke state is the transitory state labeled 4 in Fig. 1. It is experimentally difficult to characterize this either kinetically or structurally. At present, the structure can only be guessed at by an extrapolation of the properties of the adjoining structures. It seems very likely that the actin-binding cleft closes on strong binding in the top-of-powerstroke state. Comparison of the structures of the pre-powerstroke and post-rigor states with the nucleotide-free... 

The relay/converter conformation is the readout of the result of these inputs. In going from the post-rigor to pre-power states, the only signal is SW2 going from open to closed, which produces the relay kink and the converter up. To go from the pre-power to rigor states requires the /i-twist, which is triggered by actin binding and cleft closure. 

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