Conformational gating

The redox coupling of the two hemes shows different degrees of complexity in these enzymes. Pseudomonas nautica (PnNiR) shows ideal behavior and values for heme c and heme d are -1-234 mV and +199 mV, respectively. " In contrast, PpNiR shows strong heme-heme interaction resulting in hysteretic behavior attributed to kinetically gated, conformationally dependent coopera-tit vity in two-electron transfer reactions. ... 

In the post-World War II years, synthesis attained a different level of sophistication partly as a result of the confluence of five stimuli (1) the formulation of detailed electronic mechanisms for the fundamental organic reactions, (2) the introduction of conformational analysis of organic structures and transition states based on stereochemical principles, (3) the development of spectroscopic and other physical methods for structural analysis, (4) the use of chromatographic methods of analysis and separation, and (5) the discovery and application of new selective chemical reagents. As a result, the period 1945 to 1960 encompassed the synthesis of such complex molecules as vitamin A (O. Isler, 1949), cortisone (R. Woodward, R. Robinson, 1951), strychnine (R. Woodward, 1954), cedrol (G. Stork, 1955), morphine (M. Gates, 1956), reserpine (R. Woodward, 1956), penicillin V (J. Sheehan, 1957), colchicine (A. Eschenmoser, 1959), and chlorophyll (R. Woodward, 1960) (page 5). ... 

It functions by generating a gated pore in the membrane to permit passage of glucose the pore is conformationally dependent on the presence of glucose and can oscillate rapidly (about 900 times/s). 

Figure 8. A schematic for the toxin binding sites on the voltage-gated Na channel. Toxin-free open and closed conformations are drawn at the left and center. Separate sites are depicted within the membrane for activators such as BTX, VTD (A), and brevetoxin (B) these are coupled to each other and to the a-peptide toxin site (a), which is kinetically linked to the -peptide toxin site (P see ref. 20). Near the outer opening of the pore is a site (G) for STX and TTX which is affected by binding at site A and which can modify inactivation gating.

Exactly how this transporter carries noradrenaline across the neuronal membrane is not known but one popular model proposes that it can exist in two interchangeable states. Binding of Na+ and noradrenaline to a domain on its extracellular surface could trigger a conformation change that results in the sequential opening of outer and inner channel gates on the transporter. This process enables the translocation of noradrenaline from the extracellular space towards the neuronal cytosol. 

Stacking dynamics and conformational gating also provide an explanation for the distance dependence of the yield of CT between Et and ZG, a dependence which was not manifested in the CT rates [96]. Dynamic mo-... 

The acetyl choline receptor is a ligand-gated ion channel that allows cations to flow out of the neuron to initiate an action potential during neurotransmission (Fig. 9-6). When the receptor binds acetylcholine, a conformational change of the receptor opens a membrane channel that conducts ions. 

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