Photooxidation of horse and sperm-whale myoglobin sensitized by the heme group.
Abstract: The irradiation of horse and sperm-whale Fe” or Fez’ myoglobins with visible light
showed that axial ligands that render the heme diamagnetic (e.g. 02, CO or CN-) endow the
hemoproteins with a marked photosensitivity. In contrast, high-spin myoglobins are unaffected by
visible light. These findings appear to be of general validity for all hemo-proteins and are in agreement
with the involvment of the triplet state of the heme as the reactive intermediate. In all cases, the overall
photoprocess occurs within a very narrow spatial range, leading to specific modification of these
photooxidizable side chains adjacent to the chromophore. Therefore, this technique can be used to
probe the environment of the prosthetic group in hemoproteins. In particular, our data suggest that, in
horse myoglobin, histidines-93 and -64 represent the heme-linked and the distal imidazole groups,
respectively; moreover, the thioether function of methionine-131 must be nearer the heme in horse
than in sperm-whale myoglobin. The selectivity of the photoreaction can be further enhanced by a
suitable choice of the sixth ligand, and/or by controlling the pH of the irradiated solution. For example,
for both proteins, irradiation of the cyanide derivative results in specific photooxidation of the
proximal histidine, whereas irradiation of horse CO-ferromyoglobin at pH values below 6 causes
specific photooxidation of methionine-13 1. Consequently, this photooxidative procedure can also be
utilized to monitor conformational changes upon binding of the heme with different ligands, as well as
to achieve the selective modification of amino acid residues, which are usually buried inside the
protein molecule.
Publication Date: 1974-10-01 PubMed ID: 4415058DOI: 10.1111/j.1751-1097.1974.tb06588.xGoogle Scholar: Lookup
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- Journal Article
Summary
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The research article investigates the photosensitivity of horse and sperm-whale myoglobins when irradiated with visible light in the presence of certain ligands attached to the heme group. The findings suggest that such sensitivity can be manipulated to study the microenvironment of the heme group in hemoproteins and potentially observe conformational changes in proteins.
Photosensitivity of Myoglobins
- The research primarily looks into how visible light irradiation affects horse and sperm-whale myoglobins (types of hemoproteins). These proteins are known for their role in the transport and storage of oxygen in muscle cells.
- Important to the study is the presence of ligands, specifically those that make the heme group in the hemoproteins diamagnetic (such as O2, CO or CN-). This results in a marked increase in photosensitivity in the myoglobins. In contrast, high-spin myoglobins were found to be unaffected by visible light.
The Role of the Triplet State of the Heme
- The observations were consistent with the understanding that the triplet state of the heme acts as the reactive intermediate in such instances.
Probing the Environment of the Prosthetic Group
- The study implies that this photosensitivity can be leveraged to investigate the surrounding environment of the heme group within the hemoproteins.
- Specific findings suggested the relationships and positioning of histidines-93 and -64 and the thioether function of methionine-131 in horse myoglobin.
Enhancing Photoreaction Selectivity
- Additionally, the researchers found that the selectivity of the photoreactions could be manipulated by choosing suitable sixth ligands or by adjusting the pH of the solution being irradiated.
Monitoring Conformational Changes and Amino Acid Modification
- The photooxidative procedure, as demonstrated, can be applied to observe changes in the conformation of proteins upon bonding with different heme ligands.
- It can also potentially allow for the selective modification of amino acid residues usually found inside the protein molecule.
Cite This Article
APA
Folin M, Gennari G, Jori G.
(1974).
Photooxidation of horse and sperm-whale myoglobin sensitized by the heme group.
Photochem Photobiol, 20(4), 357-369.
https://doi.org/10.1111/j.1751-1097.1974.tb06588.x Publication
Researcher Affiliations
MeSH Terms
- Animals
- Hemeproteins / radiation effects
- Histidine / analysis
- Horses
- Iron / radiation effects
- Light
- Methionine / analysis
- Molecular Conformation
- Myoglobin / radiation effects
- Oxidation-Reduction
- Photochemistry
- Protein Binding
- Whales
Citations
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