The H/D exchange results of hGH at two different pHs are summarized in Fig. 12.4. There are four regions in hGH for which amide H/D exchange rates are very slow at both pH conditions tested. These regions include amino acids 15-35, 7887, 113-124, and 159-182, corresponding to the four helix bundle, a structural fold frequently found in protein hormones and other signaling proteins. High levels of deuterium incorporation are observed for the loop regions of hGH so that, at the later time points, greater than 90% deuteration is observed at both pH 7.0 and pH 2.6. Overall the H/D-Ex results for hGH correlate with the existence of secondary structure, with the helical regions of high local secondary structure showing lower rates of exchange .
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