scholarly journals The stereospecificity and catalytic efficiency of the tryptophan synthase-catalysed exchange of the α-protons of amino acids

2004 ◽  
Vol 381 (3) ◽  
pp. 847-852 ◽  
Author(s):  
Máire E. NíBEILLIÚ ◽  
J. Paul G. MALTHOUSE
Keyword(s):  
Amino Acids ◽  
Exchange Rates ◽  
Catalytic Efficiency ◽  
Deuterium Exchange ◽  
Proton Exchange ◽  
Tryptophan Synthase ◽  
Hydrogen Deuterium Exchange ◽  
Pka Values ◽  
First Order ◽  
Hydrogen Deuterium

13C-NMR has been used to follow the tryptophan synthase (EC 4.2.1.20) catalysed hydrogen–deuterium exchange of the pro-2R and pro-2S protons of [2-13C]glycine at pH 7.8. 1H-NMR has also been used to follow the tryptophan-synthase-catalysed hydrogen–deuterium exchange of the α-protons of a range of L- and D-amino acids at pH 7.8. The pKa values of the α-protons of these amino acids have been estimated and we have determined whether or not their exchange rates can be predicted from their pKa values. With the exception of tryptophan and norleucine, the stereospecificities of the first-order α-proton exchange rates are independent of the size and electronegativity of the amino acid R-group. Similar results are obtained with the second-order α-proton exchange rates, except that both L-tryptophan and L-serine have much higher stereospecificities than all the other amino acids studied.

scholarly journals The effect of different amino acid side chains on the stereospecificity and catalytic efficiency of the tryptophan synthase-catalysed exchange of the α-protons of amino acids

1996 ◽  
Vol 314 (3) ◽  
pp. 787-791 ◽  
Author(s):  
John J. MILNE ◽  
J. Paul G. MALTHOUSE
Keyword(s):  
Exchange Rate ◽  
Amino Acid ◽  
Exchange Rates ◽  
Catalytic Efficiency ◽  
Second Order ◽  
Tryptophan Synthase ◽  
Exchange Reactions ◽  
First Order ◽  
Allosteric Effector ◽  
Hydrogen Deuterium

1H-NMR has been used to follow the tryptophan synthase (EC 4.2.1.20) catalysed hydrogen–deuterium exchange of the α-protons of L- and D-alanine and -tryptophan. The first-order and second-order rate constants for exchange have been determined at pH 7.8 in the presence and absence of the allosteric effector, DL-α-glycerol 3-phosphate. In the presence of DL-α-glycerol 3-phosphate the stereospecificity of the tryptophan synthase-catalysed first-order exchange rates was in the order tryptophan > alanine > glycine. This increase in stereospecificity was largely due to the decrease in the magnitude of the first-order exchange rate of the slowly exchanged α-proton. A similar increase in the stereospecificity of the second-order exchange rates for alanine was also largely due to the decrease in the magnitude of the first-order exchange rate of the slowly exchanged α-proton of D-alanine. Adding DL-α-glycerol 3-phosphate produced an increase in the stereospecificity of the second-order exchange rate observed with alanine but no significant change in the stereospecificity of the first-order exchange rate with tryptophan. The α-subunits are shown to increase the exchange rates of the α-protons of L-alanine and L-tryptophan. We conclude that the contribution of the R-group of an amino acid to the stereospecificity of the exchange reactions of its α-proton can be similar to or larger than that of its α-carboxylate group. Possible mechanisms that could explain the stereospecificity of these exchange reactions are discussed.

scholarly journals NMR measurements of proton exchange between solvent and peptides and proteins.

1999 ◽  
Vol 46 (3) ◽  
pp. 651-663 ◽  
Author(s):  
J Wójcik ◽  
K Ruszczyńska ◽  
I Zhukov ◽  
A Ejchart
Keyword(s):  
Exchange Rates ◽  
Magnetization Transfer ◽  
Deuterium Exchange ◽  
Proton Exchange ◽  
Hydrogen Deuterium Exchange ◽  
Hydrogen Deuterium ◽  
Transfer Method ◽  
Amide Protons

Scope and limitations of the NMR based methods, equilibration and magnetization transfer, for measuring proton exchange rates of amide protons in peptides and proteins with water protons are discussed. Equilibration is applied to very slow processes detected by hydrogen-deuterium exchange after a solute is dissolved in D2O. Magnetization transfer allows to study moderately rapid processes in H2O. A number of precautions should be undertaken in order to avoid systemic errors inherent in the magnetization transfer method.

The log kexovs. log kendo correlation as a mechanistic criterion; on the mechanisms of solvolysis of norbornyl derivatives and base-catalyzed isotope exchange of norbornanones

1976 ◽  
Vol 54 (5) ◽  
pp. 678-684 ◽  
Author(s):  
Sujit Banerjee ◽  
Nick Henry Werstiuk
Keyword(s):  
Transition State ◽  
Exchange Rates ◽  
Isotope Exchange ◽  
Transition States ◽  
Substituent Effects ◽  
Proton Exchange ◽  
Hydrogen Deuterium Exchange ◽  
Rate Data ◽  
Hydrogen Deuterium ◽  
The Difference

Rate data for the acetolysis of exo-norbornyl-sulfonates have been correlated with those for the corresponding endo isomers. It is shown that the slopes of the log kexovs. log kendo plots reflect the difference in delocalization between the transition states derived from the exo and endo isomers, respectively. The log kexovs. log kendo plot, which is comprised of the parent norbornyl sufonate and its derivatives substituted at the 5, 6, and 7 positions, has a slope of 1.11 ± 0.08, which establishes that σ bridging is absent in the transition state obtained from the exo isomer. A similar analysis of base-catalyzed hydrogen–deuterium exchange rates of norbornanones reveals that exo proton exchange is more sensitive to substituent effects than the corresponding endo process.

scholarly journals Rapid and Controllable Hydrogen/Deuterium Exchange on Aromatic Rings of α-Amino Acids and Peptides

2013 ◽  
Vol 2013 (23) ◽  
pp. 5111-5116 ◽  
Author(s):  
Yuta Murai ◽  
Lei Wang ◽  
Katsuyoshi Masuda ◽  
Yasuko Sakihama ◽  
Yasuyuki Hashidoko ◽  
...  
Keyword(s):  
Amino Acids ◽  
Deuterium Exchange ◽  
Hydrogen Deuterium Exchange ◽  
Aromatic Rings ◽  
Hydrogen Deuterium
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