Rate-limiting conformational change

However, for E-P formation from E-Nas with 1.0 mM ATP and 2.0 mM ADP, observed = 4.2 X 10 s indicating that phosphoryl transfer from bound ATP to the enzyme is not rate-limiting for E-P formation from E-Nas. Their results suggest that there is likely to be a rate-limiting conformational change of the E-Nas-ATP intermediate, followed by rapid phosphoryl transfer, with kcat = 3000 s See Membrane Transport Binding Change Mechanism... 

Fiomogeneous cross-reaction electron-transfer kinetic studies suggest that many other Cu(II/I) systems obey Scheme 1. However, few Cu(II/I) systems have been subjected to sufficiently low temperature or rapid-scan CV measurements to demonstrate the presence of rate-limiting conformational changes. 

Interesting kinetic behavior is found for the adduct formation of 7-lysozyme-substituted 4-nitrobenzofurazan with OH , the attack involving the phenolic hydroxyl group of Tyr-23 of lysozyme.211 In the pH range 10.5-12.7 the formation of adduct 203 is markedly faster than that of adducts such as 204 obtained from nonproteic model compounds. The difference is attributed to a preliminary ionization of the distantly located OH of Tyr-20, followed by a rate-limiting conformational change and, finally, by a fast attack of OH. The OH nucleophile is believed to react much more... 

These results are common with proteases and also for the hydrolysis of phosphate esters catalysed by alkaline phosphatase in the latter case, there is a pitfall in that the constant value for kcat for phosphate esters is due to a rate-limiting conformational change in... 

Vande Berg, B. J., Beard, W. A., and Wilson, S. H. (2001). DNA structure and aspartate 276 influence nucleotide binding to human DNA polymerase ft. Implication for the identity of the rate-limiting conformational change. J. Biol. Chem. 276,... 

A rate-limiting conformational change of the diferric protein from closed to open configuration. 

Rapid protonation-deprotonation in the cluster, compared with the rate limiting conformational change. Nucleotide effect on H flux Conformation-dependent kinetics during ATP synthesis or hydrolysis. 

Most kinetic studies of iron release have focused on pathways involving the use of chelate ligands such as EDTA (217), pyrophosphate 218-220), phosphonates 220,221), catecholates 108,216), hydroxa-mates 120), and nitrilotriacetate (221). In many cases, simple saturation kinetics are observed, and interpreted in terms of the formation of a quaternary complex, ligand-Fe-transferrin-COs (120,122). The failure to observe this complex spectroscopically [in contrast to iron uptake studies (120)] has been explained in terms of a rate-limiting conformational change, giving a basic three-step mechanism, which is essentially the reverse of that given for iron uptake (Section V.A.l). 

In the cyt c-cyt bi complex, the lack of a strong driving force dependence of the ET rate points to a rate-limiting conformational change (124). The initial reduction of S. cerevisiae cytochrome bj by flavin was followed by ET to horse heart cytochrome c. For Fe(III)cyt c-cyt 62 ( 0.2 eV),... 

The same mechanism with a rate-limiting conformational change that results in loss of the Fe—Met has been proposed for imidazole binding to ferricyts c and C2- Imidazole... 

J by water suggesting that direct rate-limiting proton transfer takes place rather than a rate-limiting conformational change from exo to endo Dibenzo-18-crown-6 accelerates the potassium acetate catalysed proton exchange between thiophenol and solvent acetic acid, but has no effect on the methoxide catalysed exchange between thiophenol and solvent methanol. ... 

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