Involvement of lysines-72 and -79 in the alkaline isomerization of horse heart ferricytochrome c.
Abstract: Spectrophotometric titrations of five singly modified horse heart ferricytochromes c, specifically (trifluoromethyl)phenylcarbamylated (CF3PhNHCO-) or trifluoroacetylated (CF3CO-) at lysines-13, -72, and -79, were carried out. The CF3PhNHCO-Lys-13, Lys-79, and CF3CO-Lys-79 derivatives all underwent alkaline isomerization with loss of the 695-nm band to low-spin species with an apparent pK of about 8.9, as did the unmodified cytochrome. However, modification of lysine-72 appeared to alter the reaction pathway since the CF3PhNHCO-Lys-72 derivative isomerized to a high-spin form with an apparent pK of 9.3, while the CF3CO-Lys-72 derivative isomerized to a low-spin species with an apparent pK of 9.6, indicating that lysine-72 may be the normal sixth iron ligand in the native protein alkaline isomer. These results, together with those of other workers, suggest a model for the alkaline transition in which replacement of the methionine iron ligand is dependent on a number of factors, including the local availability and relative affinities of possible ligands for the heme iron and the effects of ionic and hydrophobic interactions on the tertiary structure of the molecule.
Publication Date: 1980-03-18 PubMed ID: 6245678DOI: 10.1021/bi00547a012Google Scholar: Lookup
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- Journal Article
- Research Support
- U.S. Gov't
- P.H.S.
Summary
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This study investigated the role of specific lysines in the alkaline isomerization of horse heart ferricytochrome c. The results suggest that modification of lysine-72 appears to alter the isomerization reaction pathway and indicate that lysine-72 may be a key component in the native protein alkaline isomer.
Context and Methodology
- The researchers carried out spectrophotometric titrations on five singly modified horse heart ferricytochromes c’s. These proteins were specifically carbamylated (or modified) at lyseines-13, -72, and -79. The carbamylation process involved using (trifluoromethyl)phenylcarbamyl (CF3PhNHCO-) and trifluoroacetyl (CF3CO-).
- The goal of the experiment was to study the role of those specific lysines in the alkaline isomerization of the protein. Isomerization is a process in which one molecule is transformed into another molecule which has exactly the same atoms, but the atoms have a different arrangement.
Observations and Findings
- Most of the modified proteins underwent alkaline isomerization similar to the unmodified cytochrome, leading to a loss of the 695-nm band to low-spin species with an estimated pK value of about 8.9.
- However, there was a different outcome when lysine-72 was modified. The CF3PhNHCO-Lys-72 derivative isomerized to a high-spin form with an apparent pK of 9.3, while the CF3CO-Lys-72 derivative isomerized to a low-spin species with an apparent pK of 9.6.
- This finding implies that modification at lysine-72 changes the isomerization pathway. It further proposes that lysine-72 may serve as the normal sixth iron ligand in the native protein alkaline isomer — a key piece in the structural configuration of these molecules.
Implications and Conclusions
- The results align with the work of other researchers and suggest a model for the alkaline transition. In this model, the replacement of the methionine iron ligand depends on several factors. These include the local availability and relative affinities of possible ligands for the heme iron, and the effects of ionic and hydrophobic interactions on the tertiary structure of the molecule.
- This research provides essential insights into the specific role of lysines in the isomerization process of ferricytochrome c molecules, contributing to a better understanding of the complex reactions and structural configurations involved in these biochemical reactions.
Cite This Article
APA
Smith HT, Millett F.
(1980).
Involvement of lysines-72 and -79 in the alkaline isomerization of horse heart ferricytochrome c.
Biochemistry, 19(6), 1117-1120.
https://doi.org/10.1021/bi00547a012 Publication
Researcher Affiliations
MeSH Terms
- Animals
- Cytochrome c Group
- Horses
- Hydrogen-Ion Concentration
- Lysine
- Myocardium / analysis
- Protein Conformation
- Spectrophotometry
Citations
This article has been cited 4 times.- Sivakolundu SG, Mabrouk PA. Structure-function relationship of reduced cytochrome c probed by complete solution structure determination in 30% acetonitrile/water solution. J Biol Inorg Chem 2003 May;8(5):527-539.
- Wallace CJ. Modulation of the alkaline transition in cytochrome c and cytochrome c-T by full or specific partial acetimidylation. Biochem J 1984 Feb 1;217(3):601-4.
- Boswell AP, Moore GR, Williams RJ, Harris DE, Wallace CJ, Bocieck S, Welti D. Ionization of tyrosine and lysine residues in native and modified horse cytochrome c. Biochem J 1983 Sep 1;213(3):679-86.
- Gadsby PM, Peterson J, Foote N, Greenwood C, Thomson AJ. Identification of the ligand-exchange process in the alkaline transition of horse heart cytochrome c. Biochem J 1987 Aug 15;246(1):43-54.
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