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The Secondary Structure of Human Hageman Factor (Factor XII) and its Alteration by Activating Agents

By Carl R. Mcmiliun, Hidemco Sarro, Oscar D. Ratnof and Alan G. Walton


vated by exposure to surfaces such as glass or by solu-tions of certain compounds, notably ellagic acid. Changes in the structure of Hageman factor accompany-ing activation have been examined in this study by cir-cular dichroism spectroscopy. The spectrum of unacti-vated Hageman factor in aqueous solutions suggests that its conformation is mainly aperiodic. Various perturbants altered the conformation of Hageman factor in differing ways, demonstrating the sensitivity of Hageman factor to its environment. After activation of Hageman factor with solutions of ellagic acid, a negative trough appeared in the region of the circular dichroism spectrum commonly assigned to tyrosine residues, along with other minor changes in the peptide spectral region. Some of these changes are similar to changes that occurred upon partial neutraliza-tion of the basic residues at alkali pH. Activation of Hageman factor by adsorption to quartz surfaces (in an aqueous environment) also produced changes simi-lar to those in the ellagic acid-activated Hageman factor, including the negative ellipticity in the tyrosine region. These observations suggest that the activation process may be related to a change in status of some of the basic amino acid residues, coupled with a specific change in the environment of some tyrosine residues. The im-portance of these changes during the activation process remains to be determined. The sensitivity of Hageman factor to its environment is consistent with the view that the initiation of clotting by exposure of plasma to appropriate agents is brought about by alterations in the conformation of Hageman factor that occur in th

Year: 2016
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