Amide hydrogen exchange rates

Fig. 23. Dependence on log water activity of log ratio of powder to solution amide hydrogen exchange rate for lysozyme. Log rate ratio data for pH 2 (bottom) to pH 10 (top) are given as a function of log(/ /Po). The slopes of the lines give the order of the protein exchange reaction with respect to water. The slopes from least-squares linear regression are the following pH 2, 2.57 pH 3, 2.90 pH 5, 3.14 pH 7, 3.14 and pH 10, 2.53. Displacement along the log rate ratio axis is arbitrary. Numbers indicate some of the H m values for which rate ratios were determined. From Schinkel et at. (1985).

Amide hydrogen exchange rates are also dependent on temperature, with approximately three times increase in both acid- and base-catalyzed exchange rates for every increment of 10°C [9] and is described in more detail in Section 1.2.2 (see also Figure 1.6). To minimize variations in hydrogen exchange between multiple experiments, temperature should be precisely controlled ( 2°C)... 

Thevenon-Emeric, G., Kozlowski, J., Zhang, Z., Smith, D.L. (1992) Determination of amide hydrogen exchange rates in peptides by mass spectrometry. Anal Chem, 64 (20), 2456-2458. 

Molday, R.S., Kallen, R.G. (1972) Substituent effects on amide hydrogen exchange rates in aqueous... 

The number of NMR parameters available for measurement is rather small, consisting of the chemical shift, relaxation rates (/1 and lo), scalar (J) couplings, dipolar (D) couplings, cross-relaxation rates (the NOE), and hydrogen exchange rates. All of these have been quantified for many of the amide protons of A131 A, and most of the data suggest the presence of little persistent structure. 

Amide proton temperature coefficients and hydrogen exchange rates can provide information about hydrogen-bonding interactions and solvent sequestration in unfolded or partly folded proteins (Dyson and Wright, 1991). Abnormally low temperature coefficients, relative to random coil values, are a clear indication of local structure and interactions. 

Several features affect the rate of amide hydrogen exchange, which reflect the protein s structure and dynamic properties. These include an amide s participation in hydrogen bonding [36], its distance from the protein surface [3], and the... 

Formalisms to relate the observed rates of amide hydrogen exchange to thermodynamic stabilization of proteins have been developed [38]. Amide hydrogens of proteins in the native, folded state are proposed to exchange according to the following equation ... 

Amide hydrogen exchange in protein powders depends weakly on water activity, and its hydration dependence is complete within the low-hydration region (0.15 A). Apparently, the rate-determining step for the exchange of buried hydrogens is not much influenced by the protein surface. This is unexplained. 

Figure 14.5. HX reveals a temperature-dependent transition in mobility, (a) Arrhenius plot for the oxidation of protonated (circles) or deuterated (squares) benzyl alcohol by htADH. The discontinuity at 30 °C indicates a transition in activation energy for the reaction, (b) Weighted averaged HX rate constant ( HX(wA)) fot peptides from htADH plotted versus 1 /T show/s discontinuities at 30 °C in five peptides. The w/eighted averaged kHX is defined as (A(ti + 6(t2 + Ck )/NH where NH is the total number of amide hydrogens in the peptide, and A, B, and C are the number of amide hydrogens exchanging with rate...

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