The reactivity of the sulfhydril group beta-93 has been used as a probe of the conformation of beta chains in native human hemoglobin, globin and intermediate compound II, which consists of a hemoglobin with heme on alpha chains only. The study has been extended to the reactivity of the SH groups of isolated beta chains. Stopped-Flow analysis of the reaction of the SH groups of the individual molecules with parahydroxymer-curibenzoate has been performed and the values of the second order rate constants, the pH dependence and the activation energy of the reactions have been used as criteria to distinguish the different reactivities. The results indicate that the major contributions to the conformation of beta chains in native human hemoglobin derive from alpha chain—beta chain interaction and from the insertion of heme into beta chain heme-pockets. The insertion of heme in the alpha chain heme-pockets appears to have only minor effects on beta chain conformation.
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Con il contributo del Ministero per i Beni e le Attività Culturali