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出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2014/06/07 19:57:29」(JST)
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Photoprotection is a group of mechanisms that nature has developed to minimize the damage that the human body suffers when exposed to UV radiation. This damage mostly occurs in the skin, but the rest of the body can be affected by the oxidative stress caused by UV light.
Photoprotection of the human skin is achieved by extremely efficient internal conversion of DNA, proteins and melanin. Internal conversion is a photochemical process that converts the energy of the UV photon into small, harmless amounts of heat. If the energy of the UV photon were not transformed into heat, then it would lead to the generation of free radicals or other harmful reactive chemical species (e.g. singlet oxygen, or hydroxyl radical).
In DNA this photoprotective mechanism evolved four billion years ago at the dawn of life.[1] The purpose of this extremely efficient photoprotective mechanism is to prevent direct DNA damage and indirect DNA damage. The ultrafast internal conversion of DNA reduces the excited state lifetime of DNA to only a few femtoseconds (10−15s)—this way the excited DNA does not have enough time to react with other molecules.
For melanin this mechanism has developed later in the course of evolution. Melanin is such an efficient photoprotective substance that it dissipates more than 99.9% of the absorbed UV radiation as heat. [2] This means that less than 0.1% of the excited melanin molecules will undergo harmful chemical reactions or produce free radicals.
Artificial melanin
The cosmetic industry claims that the UV filter acts as an "artificial melanin". But those artificial substances used in sunscreens do not efficiently dissipate the energy of the UV photon as heat. Instead these substances have a very long excited state lifetime. [3]
In fact, the substances used in sunscreens are often used as photosensitizers in chemical reactions. (see Benzophenone).
This discrepancy between melanin and sunscreen ingredients is one of the reasons for the increased melanoma risk that can be found in sunscreen users compared to non-users. (see sunscreen) Oxybenzone, titanium oxide and octyl methoxycinnamate are photoprotective agents used in many sunscreens, providing broad-spectrum UV coverage, including UVB and short-wave UVA rays.[4][5]
UV-absorber |
other names |
percentage of molecules that dissipate the photon energy (quantum yield: Φ ) [3]
|
molecules not dissipating the energy quickly |
DNA |
|
> 99.9% |
< 0.1% |
natural melanin |
|
> 99.9% |
< 0.1% |
2-phenylbenzimidazole-5-sulfonic acid |
PBSA, Eusolex 232, Parsol HS, |
|
|
2-ethylhexyl 4-dimethylaminobenzoate |
Padimate-O, oxtyldimethyl PABA, OD-PABA |
0.1 = 10% |
90% |
4-Methylbenzylidene camphor |
(4-MBC), (MBC), Parsol 5000, Eusolex 6300 |
0.3 = 30% |
70% |
4-tert-butyl-4-methoxydibenzoyl-methane |
(BM-DBM), Avobenzone, Parsol 1789, Eusolex 9020 |
|
|
Menthyl Anthranilate |
(MA), Menthyl-2-aminobenzoate, meradimate |
0.6 = 60% |
40% |
Ethylhexyl methoxycinnamate |
(2-EHMC), (EHMC), EMC, Octyl methoxycinnamate, OMC, Eusolex 2292, Parsol |
0.81 = 81% |
19% |
See also
- Sunscreen
- Photocarcinogen
- Direct DNA damage
- Indirect DNA damage
References
- ^ "ultrafast internal conversion of DNA". Retrieved 2008-02-13.
- ^ Meredith, Paul; Riesz, Jennifer (2004). "Radiative Relaxation Quantum Yields for Synthetic Eumelanin". Photochemistry and photobiology 79 (2): 211–216. doi:10.1562/0031-8655(2004)079<0211:RCRQYF>2.0.CO;2. ISSN 0031-8655. PMID 15068035.
- ^ a b Cantrell, Ann; McGarvey, David J; (2001). "3(Sun Protection in Man)". Comprehensive Series in Photosciences 495: 497–519. CAN 137:43484.
- ^ Burnett, M. E. and Wang, S. Q. (2011), Current sunscreen controversies: a critical review. Photodermatology, Photoimmunology & Photomedicine, 27: 58–67
- ^ Serpone N, Salinaro A, Emeline AV, Horikoshi S, Hidaka H, Zhao JC. 2002. An in vitro systematic spectroscopic examination of the photostabilities of a random set of commercial sunscreen lotions and their chemical UVB/UVA active agents. Photochemical & Photobiological Sciences 1(12): 970-981.
UpToDate Contents
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English Journal
- Disentangling two non-photochemical quenching processes in Cyclotella meneghiniana by spectrally-resolved picosecond fluorescence at 77K.
- Chukhutsina VU1, Büchel C2, van Amerongen H3.
- Biochimica et biophysica acta.Biochim Biophys Acta.2014 Jun;1837(6):899-907. doi: 10.1016/j.bbabio.2014.02.021. Epub 2014 Feb 27.
- Diatoms, which are primary producers in the oceans, can rapidly switch on/off efficient photoprotection to respond to fast light-intensity changes in moving waters. The corresponding thermal dissipation of excess-absorbed-light energy can be observed as non-photochemical quenching (NPQ) of chlorophy
- PMID 24582663
- Characterizing photoinhibition and photosynthesis in juvenile-red versus mature-green leaves of Jatropha curcas L.
- Ranjan S1, Singh R1, Singh M2, Pathre UV1, Shirke PA3.
- Plant physiology and biochemistry : PPB / Société française de physiologie végétale.Plant Physiol Biochem.2014 Jun;79:48-59. doi: 10.1016/j.plaphy.2014.03.007. Epub 2014 Mar 13.
- The new leaves of Jatropha curcas (L.) appear dark red in colour due to the presence of anthocyanin pigments, these leaves subsequently turn green on maturity. The aim of the study was to characterize the photosynthetic efficiency of the juvenile red and mature green leaves and to understand the pos
- PMID 24681755
- Photoprotective characteristics of natural antioxidant polyphenols.
- Stevanato R1, Bertelle M2, Fabris S3.
- Regulatory toxicology and pharmacology : RTP.Regul Toxicol Pharmacol.2014 Jun;69(1):71-7. doi: 10.1016/j.yrtph.2014.02.014. Epub 2014 Mar 5.
- Fourteen natural polyphenols belonging to the classes of stilbenes, flavonoids and hydroxycinnamic acid derivatives, have been investigated in order to verify the combination of their photoprotective characteristics with their antioxidant properties. To this purpose, sun protection factor (SPF), UVA
- PMID 24607767
Japanese Journal
- Structure and energy transfer pathways of the plant photosystem I-LHCI supercomplex
- Photosynthetic response to fluctuating environments and photoprotective strategies under abiotic stress (JPR Symposium : Responses of the Photosynthetic Systems to Spatio-temporal Variations in Light Environments : Scaling and Eco-devo Approaches)
- 植物光化学系I-集光性アンテナ複合体I超複合体の結晶構造
Related Links
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