HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Sebring, E. D. Articles by Steinhardt, J. Search for Related Content PubMed PubMed Citation Articles by Sebring, E. D. Articles by Steinhardt, J. Social Bookmarking                      What's this?

Stabilization of Horse Globin by Protoporphyrin IX and Hemin

From the ¹ From the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20014, and the Department of Chemistry, Georgetown University, Washington, D. C. 20007

When the kinetics of unmasking of certain inaccessible acid-binding groups in native horse ferrihemoglobin (Hb⁺) is measured in a pH-stat, the results are essentially identical with those obtained by spectrophotometric methods of following denaturation and regeneration. The pH-stat method has therefore been applied to determine the pH profile of the denaturation kinetics and equilibria of globin at a number of temperatures. The acid denaturation of globin is first order and has the same dependence on pH as Hb⁺, but globin reacts at any pH about 2000 times more rapidly than Hb⁺; the measurements are therefore made at about 1 pH unit higher than with Hb⁺. As with apomyoglobin, fewer groups in globin are unmasked than when intact ferrihemoglobin is acid-denatured; it appears that as many as 16 groups may be unmasked when hemin is removed from Hb⁺. Hb⁺ reconstituted from globin and hemin has the same absorption spectrum and kinetic properties as the initial material.

When protoporphyrin IX (which contains no iron) rather than hemin is complexed with globin under certain narrowly critical conditions, the resulting complex approaches Hb⁺ in its kinetic stability. The conclusion is drawn that Hb⁺, unlike such ferrohemoglobins as COHb, derives little of its stability from the highly polar (ionic) iron-nitrogen bond in the ferric protein. Under other conditions of formation, protoporphyrin-globin may consist of more than one complex, each of which has a different stability.

Globin and the most stable protoporphyrin-globin complexes behave differently from Hb⁺ with respect to the effects of temperature on their denaturation rates and equilibria. Two denaturation paths exist in the case of Hb⁺, one of which prevails at low temperatures and the other at temperatures above 15°. Globin appears to denature by the path characteristic of Hb⁺ at low temperatures, and protoporphyrin-globin by the reaction path characteristic of Hb⁺ above 15°.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				O. Daltrop and S. J. Ferguson In Vitro Studies on Thioether Bond Formation between Hydrogenobacter thermophilus Apocytochrome c552 with Metalloprotoporphyrin Derivatives J. Biol. Chem., October 29, 2004; 279(44): 45347 - 45353. [Abstract] [Full Text] [PDF]

				C Kirmaier, D Gaul, R DeBey, D Holten, and C. Schenck Charge separation in a reaction center incorporating bacteriochlorophyll for photoactive bacteriopheophytin Science, February 22, 1991; 251(4996): 922 - 927. [Abstract] [PDF]