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<p>The zero- and double-quantum methyl TROSY Hahn-echo and the methyl <sup>1</sup>H-<sup>1</sup>H dipole-
dipole cross-correlation nuclear magnetic resonance experiments enable estimation of multiple
quantum chemical exchange broadening in methyl groups in proteins. The two relaxation rate
constants are established to be linearly dependent using molecular dynamics simulations and
empirical analysis of experimental data. This relationship allows chemical exchange broadening
to be recognized as an increase in the Hahn-echo relaxation rate constant. The approach is
illustrated by analyzing relaxation data collected at three temperatures for <i>E. coli </i>ribonuclease HI
and by analyzing relaxation data collected for different cofactor and substrate complexes of <i>E.
coli </i>AlkB.
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