| Autor: |
Oleksandr Kokhan, Aidan M. McKenzie, C. Alexander Hudson, Daniel R. Marzolf |
| Rok vydání: |
2017 |
| Předmět: |
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| Zdroj: |
Biophysical Journal. 112:442a |
| ISSN: |
0006-3495 |
| DOI: |
10.1016/j.bpj.2016.11.2359 |
| Popis: |
Due to their rich and tunable spectral and redox properties as well as relatively simple synthesis protocols, water-soluble porphyrins are promising candidates as photosensitizers for artificial photosynthesis. Quenching of porphyrin static fluorescence by monoheme horse heart cytochrome (cyt) c is a well-known phenomenon. It is attributed to the fast charge separation (CS), though the CS state has not been observed. Similarly, we found quenching of static fluorescence of porphyrins in the presence of PpcA, a 3-heme c-type cytochrome from the cyt c7 family from Geobacter sulfurreducens. In this report using ultrafast visible transient absorbance spectroscopy we demonstrate that the excited state of protein-bound zinc tetraphenyl sulfonated porphyrin (ZnTPPS) decays with an apparent time constant of about 200 ps in the presence of cyt c and approximately 20 ps in the presence of PpcA. However, the spectral changes are dominated by the features of porphyrin singlet and triplet states. Only a small fraction of photosensitizer excited state energy is retained in the CS state suggesting a competing energy transfer mechanism. Unbound fraction of ZnTPPS shows triplet quenching as a second order process with similar low CS state yields for both cyt c and PpcA. Heteronuclear NMR and all-atom molecular dynamics simulations reveal the likely surface binding sites for ZnTPPS. However, small angle X-ray scattering measurements demonstrate propensity of ZnTPPS to induce formation of protein multimers under experimental conditions typical for our experiments. There results demonstrate an unexpected complexity of ZnTPPS binding interactions and photochemistry with c-type cytochromes and suggest the presence of a competing dominant energy transfer process. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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