Reversibility restoring energy

Reaction energy, 98 Le Cliate-lier s principle of, 304 Reciprocal relations, 104 Reduced magnitudes, 229 Reech s theorem, 118, 144 Refrigerator, 53 Restoration of energy, 68 Reversibility, 48... 

Fig. Id represents the ionic changes and reversal of polarity of the membrane when the nerve is stimulated. Na+ ions enter the membrane ahead of the electrical charge and K+ ions pass out at the peak of the potential reversal.1 Fig. le shows how the ionic interchange is related to the action potential (or magnitude of polarity change). It must be stressed that the actual percentage changes of concentration are very small indeed. The exact nature of the restoration of the original concentration of ions is not completely known. Obviously a source of energy is required, and this is considered to be derived from the metabolism of the cell.

In the in-line push-pull mechanisms of Rabin and Roberts, the highest energy transition state may be either the pentacovalent intermediate or the alkoxide (hydroxide) state with 02 or 05" deprotonated but not bonded to P. Incipient deprotonation of 02 in an activated state is equivalent. Protonation of X or Y or nearby positive charge could stabilize the pentacovalent intermediate. Removal of either could facilitate formation of the alkoxide in the breakdown of the intermediate. Restoration of the initial state of the enzyme is required in this mechanism and could be rate limiting. In the adjacent (pseudorotation) models of Witzel, Hammes, Usher, or Wang protonation of X or Y would be required to allow one of the two pseudomers to exist. In step 1 this requirement (and thus perhaps a rate limiting process) applies to the attack by 02. Deprotonation would force or facilitate reversal or pseudorotation to... 

The stable products that escaped the geminate backward reaction are not survived forever. They meet in the bulk with partners separated from other pairs, and in these encounters the reverse transfer of energy or charge continues to the point of their disappearance. This bimolecular reaction is represented by terms that are proportional to Na in Eqs. (3.114) and (3.127). These terms omitted in Eqs. (3.135) as insignificant during the geminate stage of transfer, will be restored and discussed in Section VIII. 

Nonequilibrium, time-dependent processes manifest mosdy as transport and relaxation (Wunderlich, 1990) describe polysaccharide events. The terminal outcome of transport is a change in position (potential energy), and that of relaxation is restoration exactly or approximately to an initial energy state. Because polysaccharide events are nonequilibrium processes, the addition or subtraction of energy is necessary for reversibility. 

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