Motors rotary

A Membrane-Located ATP Synthase Functions as a Rotary Motor to Form ATP... 

Campbell, P.N., Smith, A.D. and Peters, T.J. (2005) Biochemistry Illustrated Biochemistry and Molecular Biology in the Post-Genomic Era, 5th edition, Elsevier, London and Oxford, 242 pp. Capaldi, R. and Aggeler, R. (2002) Mechanism of FjF0-type ATP synthase, a biological rotary motor, TIBS, 27, 154-160. 

A. Kazaryan, Z. G. Lan, L. V. Schafer, M. Filatov, and W. Thiel. Surface hopping excited-state dynamics study of the photoisomerization of a light-driven fluorene molecular rotary motor, J. Chem. Theory Comput., 1 2189-2199 (2011). 

Brake, hydraulic, and recoil-cylinder fluids fall in much the same field of operating conditions. These are employed in systems in which operating units are exposed to low temperatures, and in practically all cases the connecting tubing lines are so exposed. Temperatures are not likely to go very high, but for aviation, temperatures as low as —70° F. may be frequent. Practically all brake systems and many hydraulic systems employ reciprocating units packed with synthetic rubbers. Hydraulic systems employ rotary pumps and often rotary motors these cannot be soft packed but are only capillary-sealed—i.e., close clearances. These pumps and motors drop in volumetric efficiency as viscosity falls. 

The shaft and rings at the base of the flagellum make up a rotary motor that has been called a "proton turbine." Protons ejected by electron transfer flow back into the cell through the turbine, causing rotation of the shaft of the flagellum. This motion differs fundamentally from the motion of muscle and of eukaryotic flagella and cilia, for which ATP hydrolysis is the energy source. 

N-terminals of the /3 subunits. At the other end, a cysteine residue was introduced into the exposed tip of the y subunit, which was coupled to biotin, and then attached to a fluorescently labeled actin filament via a streptavidin linker. The ATP-dependent anticlockwise rotation of the 1- to 3-p.m-long actin filaments was seen in a fluorescence microscope.94 Smaller probes show that the rotation is consistent with the turnover of ATP by the FrATPase, which is consistent with a three-step motor.95,96 This implies that ATP synthesis requires that the y subunit be cranked in a clockwise direction by a rotary motor in F,. 

Parallels between everyday mechanisms and cellular processes extend also to myosin head groups racheting to actin subunits to produce the sliding filaments of skeletal muscle (see Perry, 1997), rotary motors for bacterial flagella (see Armitage, 1997) or movements along microtubules, powered by the proton motive force or ATP (see also Block, 1997). The existence of a mitochondrial rotary motor has recently been established. Boyer s proposal that the y subunit of the mitochondrial ATP synthase rotated within the other subunits has been vindicated by X-ray crystallography (Walker, 1997) and direct demonstration of the rotation. 

A unique feature of the F/V/A-ATPases is that they are rotary molecular motor enzymes. This has been shown by experiment for members of the F-and V-ATPase subfamilies and is generally assumed to be true for the closely related A-ATPases as well. The two enzymatic processes, ATP synthesis/hydrolysis and ion translocation, are coupled via a rotational motion of a central domain of the complex (the rotor) relative to a static domain (the stator). The A-, F-, and V-ATPases represent the smallest rotary motors found in the living cell so far. Most of what we know about the structure and mechanism of these microscopic energy converters comes from studies conducted with the F-ATPase. In the following review, current structural knowledge for all three members of the family of F-, V-,... 

Jiang, W., Hermolin, J., and Fillingame, R. H. (2001). The preferred stoichiometry of c subunits in the rotary motor sector of Escherichia coli ATP synthase is 10. Proc. Natl. Acad. Sci. USA 98, 4966-4971. 

Tsunoda, S. P., Rodgers, A. J., Aggeler, R., Wilce, M. C., Yoshida, M., and Capaldi, R. A. (2001b). Large conformational changes of the e subunit in the bacterial F F0 ATP synthase provide a ratchet action to regulate this rotary motor enzyme. Proc. Natl. Acad. Sci. USA 98, 6560-6564. 

Another example of a rotary motor is that of bacterial flagella, 23 which are responsible for bacterial motility. 

Fig. 2 A schematic representation of ATP synthase, a biological rotary motor, y (and c) are mobile whereas the aggregate a3 33 is fixed to the membrane and constitutes the stator of the motor.

Towards Rotary Motors Pirouetting of a Two-coordinate Ring on its Thread... 

Finally, the making of real motors at the molecular level remains a challenge. Not only will the motion have to be continuous, in the sense that cyclic processes, with a turnover, are required, but directionality will be essential. This is especially true for molecular ensembles aimed at mimicking the dynamic properties of ATP synthase. Although still relatively remote from continuous directional rotary motion, one interesting chemical system with behavior reminiscent of rotary motors has recently been proposed.11041 For a photochemical driven unindirectional rotor,11051 see Chapter 5. Other systems, based on related or different principles, will no doubt be reported in the future. 

Figure 4.3 The enzyme ATP synthase synthesizes the chemical energy-storage compound known as ATP. One of this complex enzyme s two rotary motors is the FI motor (shown in the image above), a chemical motor that creates the ATP.

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