| Records |
Author  |
Abbruzzetti, S.; Viappiani, C.; Sinibaldi, F.; Santucci, R. |
| Title |
Kinetics of histidine dissociation from the heme Fe(III) in N-fragment (residues 1-56) of cytochrome c |
Type |
Journal Article |
| Year |
2004 |
Publication |
The Protein Journal |
Abbreviated Journal |
Protein J |
| Volume |
23 |
Issue |
8 |
Pages |
519-527 |
| Keywords |
Animals; Cytochromes c/*chemistry; Enzyme Activation; Histidine/*chemistry; Horses; Hydrogen-Ion Concentration; Kinetics; Lasers; Ligands; Peptide Mapping; Photolysis; Spectrophotometry |
| Abstract |
We have here investigated the dissociation kinetics of the His side chains axially ligated to the heme-iron in the ferric (1-56 residues) N-fragment of horse cyt c. The ligand deligation induced by acidic pH-jump occurs as a biexponential process with different pre-exponential factors, consistent with a structural heterogeneity in solution and the presence of two differently coordinated species. In analogy with GuHCl-denatured cyt c, our data indicate the presence in solution of two ferric forms of the N-fragment characterized by bis-His coordination, as summarized in the following scheme: His18-Fe(III)-His26 <==> His18-Fe(III)-His33. We have found that the pre-exponential factors depend on the extent of the pH-jump. This may be correlated with the different pKa values shown by His26 and His33; due to steric factors, His26 binds to the heme-Fe(III) less strongly than His33, as recently shown by studies on denatured cyt c. Interestingly, the two lifetimes are affected by temperature but not by the extent of the pH-jump. The lower pKa for the deligation reaction required the use of an improved laser pH-jump setup, capable of inducing changes in H+ concentration as large as 1 mM after the end of the laser pulse. For the ferric N-fragment, close activation entropy values have been determined for the two histidines coordinated to the iron; this result significantly differs from that for GuHCl-denatured cyt c, where largely different values of activation entropy were calculated. This underlines the role played by the missing segment (residues 57-104) peptide chain in discriminating deligation of the “nonnative” His from the sixth coordination position of the metal. |
| Address |
Dipartimento di Fisica, Universita degli Studi di Parma, Parco Area delle Scienze 7/A 43100 Parma, Italy |
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Place of Publication |
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Editor |
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| Language |
English |
Summary Language |
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Original Title |
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Series Title |
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Abbreviated Series Title |
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| Series Volume |
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Series Issue |
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Edition |
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| ISSN |
1572-3887 |
ISBN |
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Expedition |
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| Notes |
PMID:15648974 |
Approved |
no |
| Call Number |
Equine Behaviour @ team @ |
Serial |
3770 |
| Permanent link to this record |
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| Author |
Miksovska, J.; Larsen, R.W. |
| Title |
Photothermal studies of pH induced unfolding of apomyoglobin |
Type |
Journal Article |
| Year |
2003 |
Publication |
Journal of Protein Chemistry |
Abbreviated Journal |
J Protein Chem |
| Volume |
22 |
Issue |
4 |
Pages |
387-394 |
| Keywords |
Acoustics; Animals; Apoproteins/*chemistry/metabolism; Circular Dichroism; Horses; Myocardium/chemistry; Myoglobin/*chemistry/metabolism; Photolysis; Protein Conformation/radiation effects; Protein Denaturation/radiation effects; *Protein Folding; Temperature; Thermodynamics |
| Abstract |
Conformational dynamic and enthalpy changes associated with pH induced unfolding of apomyoglobin were studied using photoacoustic calorimetry and photothermal beam deflection methods. The transition between the native state and the I intermediate was induced by a nanosecond pH jump from o-nitrobenzaldehyde photolysis. Deconvolution of photoacoustic waves indicates two kinetic processes. The fast phase (T < 50 ns) is characterized by a volume expansion of 8.8 ml mol(-1). This process is followed by a volume contraction of about -22 ml mol(-1) (tau approximately 500 ns). Photothermal beam deflection measurements do not reveal any volume changes on the time scale between approximately 100 micros and 5 ms. We associate the volume contraction with structural changes occurring during the transition between the native state and the I intermediate. The lack of any processes on the ms time scale may indicate the absence of structural events involving larger conformational changes of apomyoglobin after the pH jump. |
| Address |
Department of Chemistry, University of South Florida, Tampa, Florida 33620, USA |
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Place of Publication |
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| Language |
English |
Summary Language |
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Original Title |
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Series Title |
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Abbreviated Series Title |
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Series Issue |
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Edition |
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| ISSN |
0277-8033 |
ISBN |
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Medium |
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Expedition |
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Conference |
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| Notes |
PMID:13678303 |
Approved |
no |
| Call Number |
Equine Behaviour @ team @ |
Serial |
3780 |
| Permanent link to this record |
