Document Detail

Nanosecond optical spectra of iron-cobalt hybrid hemoglobins: geminate recombination, conformational changes, and intersubunit communication.
MedLine Citation:
PMID:  4027219     Owner:  NLM     Status:  MEDLINE    
Hybrid hemoglobins were prepared in which cobalt was substituted for the heme iron in either the alpha or beta subunits. Transient optical absorption spectra were measured at room temperature for these hybrids at time intervals between 0 and 50 ms following photodissociation of the carbon monoxide complex with 10-ns laser pulses. The cobalt porphyrins do not bind carbon monoxide, making it possible to investigate the time-resolved response of the cobalt-containing subunits to photodissociation of carbon monoxide in the iron-containing subunits. At the same time the response of the iron-containing subunits to the photolysis event can be studied, permitting an independent determination of the kinetics of ligand rebinding and conformational changes in the alpha and beta subunits of an intact tetramer. The data were analyzed by using singular-value decomposition to obtain the kinetic progress curve for ligand rebinding, the deoxyheme and cobalt porphyrin spectral changes, and the time course of these spectral changes. The geminate rebinding kinetics following photodissociation of alpha(Co)2 beta(Fe-CO)2 were very similar to those found unsubstituted hemoglobin, alpha(Fe-CO)2 beta(Fe-CO)2, indicating equivalence of the geminate kinetics for alpha and beta subunits within the R-state tetramer. The results for alpha(Fe-CO)2 beta(Co)2 were consistent with this conclusion, even though the analysis was complicated by the presence of comparable populations of R- and T-state species. Comparison of the deoxyheme spectral changes and relaxation times among the three molecules indicated that both alpha and beta subunits contribute to the deoxyheme spectral changes that signal tertiary and quaternary conformational changes in the unsubstituted tetramer. The response of the cobalt porphyrins to photodissociation was similar in the two hybrids. No structural changes were detected in the cobalt-containing subunits until the second tertiary conformational change in the iron-containing subunits observed at 1-2 microseconds. Much larger structural changes, as judged by the amplitude of the spectral changes, occurred in the cobalt-containing subunits concomitant with the R----T quaternary change at about 20 microseconds.
J Hofrichter; E R Henry; J H Sommer; R Deutsch; M Ikeda-Saito; T Yonetani; W A Eaton
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Biochemistry     Volume:  24     ISSN:  0006-2960     ISO Abbreviation:  Biochemistry     Publication Date:  1985 May 
Date Detail:
Created Date:  1985-09-27     Completed Date:  1985-09-27     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  0370623     Medline TA:  Biochemistry     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  2667-79     Citation Subset:  IM    
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MeSH Terms
Cobalt / blood*
Hemoglobins / metabolism*
Iron / blood*
Macromolecular Substances
Protein Binding
Protein Conformation
Protein Multimerization
Time Factors
Grant Support
Reg. No./Substance:
0/Hemoglobins; 0/Ligands; 0/Macromolecular Substances; 0/iron-cobalt hybrid hemoglobin; 7439-89-6/Iron; 7440-48-4/Cobalt

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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