Фотозащита
Фотозащита - это биохимический процесс, который помогает организмам справляться с молекулярным повреждением, вызванным солнечным светом . Растения и другие кислородо -фототрофы разработали набор фотозащитных механизмов для предотвращения фотоингибирования и окислительного стресса, вызванного избыточным или колеблющимся условиями освещения. У людей и других животных также развились фотозащитные механизмы, чтобы избежать ультрафиолетового фотодопа до кожи, предотвратить повреждение ДНК и минимизировать последующие эффекты окислительного стресса.
В фотосинтетических организмах
[ редактировать ]У организмов, которые выполняют кислородный фотосинтез , избыточный свет может привести к фотоингибированию или фотоинактивации реакционных центров , процесс, который не обязательно включает в себя химическое повреждение. Когда фотосинтетические антенные пигменты, такие как хлорофилл, возбуждаются в результате поглощения света, непродуктивные реакции могут возникать путем переноса заряда в молекулы с непарными электронами. Поскольку кислородо -фототрофы генерируют O 2 в качестве побочного продукта от фотокатализированного расщепления воды (H 2 O) , фотосинтетические организмы имеют особый риск образования реактивных форм кислорода . [ Цитация необходима ]
Следовательно, разнообразный набор механизмов развился в фотосинтетических организмах, чтобы смягчить эти потенциальные угрозы, которые усугубляются при высоком излучении, колеблющихся условиях освещения, в неблагоприятных условиях окружающей среды, таких как холод или засуха, и при переживании дефицита питательных веществ, которые вызывают дисбаланс между энергетикой. раковины и источники.
In eukaryotic phototrophs, these mechanisms include non-photochemical quenching mechanisms such as the xanthophyll cycle, biochemical pathways which serve as "relief valves", structural rearrangements of the complexes in the photosynthetic apparatus, and use of antioxidant molecules. Higher plants sometimes employ strategies such as reorientation of leaf axes to minimize incident light striking the surface. Mechanisms may also act on a longer time-scale, such as up-regulation of stress response proteins or down-regulation of pigment biosynthesis, although these processes are better characterized as "photoacclimatization" processes.
Cyanobacteria possess some unique strategies for photoprotection which have not been identified in plants nor in algae.[1] For example, most cyanobacteria possess an Orange Carotenoid Protein (OCP), which serves as a novel form of non-photochemical quenching.[2] Another unique, albeit poorly-understood, cyanobacterial strategy involves the IsiA chlorophyll-binding protein, which can aggregate with carotenoids and form rings around the PSI reaction center complexes to aid in photoprotective energy dissipation.[3] Some other cyanobacterial strategies may involve state-transitions of the phycobilisome antenna complex[4] , photoreduction of water with the Flavodiiron proteins,[5] and futile cycling of CO2[6] .
In plants
[edit]It is widely known that plants need light to survive, grow and reproduce. It is often assumed that more light is always beneficial; however, excess light can actually be harmful for some species of plants. Just as animals require a fine balance of resources, plants require a specific balance of light intensity and wavelength for optimal growth (this can vary from plant to plant). Optimizing the process of photosynthesis is essential for survival when environmental conditions are ideal and acclimation when environmental conditions are severe. When exposed to high light intensity, a plant reacts to mitigate the harmful effects of excess light.
To best protect themselves from excess light, plants employ a multitude of methods to minimize harm inflicted by excess light. A variety of photoreceptors are used by plants to detect light intensity, direction and duration. In response to excess light, some photoreceptors have the ability to shift chloroplasts within the cell farther from the light source thus decreasing the harm done by superfluous light.[7] Similarly, plants are able to produce enzymes that are essential to photoprotection such as Anthocyanin synthase. Plants deficient in photoprotection enzymes are much more sensitive to light damage than plants with functioning photoprotection enzymes.[8] Also, plants produce a variety of secondary metabolites beneficial for their survival and protection from excess light. These secondary metabolites that provide plants with protection are commonly used in human sunscreen and pharmaceutical drugs to supplement the inadequate light protection that is innate to human skin cells.[9] Various pigments and compounds can be employed by plants as a form of UV photoprotection as well.[10]
Pigmentation is one method employed by a variety of plants as a form of photoprotection. For example, in Antarctica, native mosses of green color can be found naturally shaded by rocks or other physical barriers while red colored mosses of the same species are likely to be found in wind and sun exposed locations. This variation in color is due to light intensity. Photoreceptors in mosses, phytochromes (red wavelengths) and phototropins (blue wavelengths), assist in the regulation of pigmentation. To better understand this phenomenon, Waterman et al. conducted an experiment to analyze the photoprotective qualities of UVACs (Ultraviolet Absorbing Compounds) and red pigmentation in antarctic mosses. Moss specimens of species Ceratodon purpureus, Bryum pseudotriquetrum and Schistidium antarctici were collected from an island region in East Antarctica. All specimens were then grown and observed in a lab setting under constant light and water conditions to assess photosynthesis, UVAC and pigmentation production. Moss gametophytes of red and green varieties were exposed to light and consistent watering for a period of two weeks. Following the growth observation, cell wall pigments were extracted from the moss specimens. These extracts were tested using UV–Vis spectrophotometry which uses light from the UV and visible spectrum to create an image depicting light absorbance. UVACs are typically found in the cytoplasm of the cell; however, when exposed to high-intensity light, UVACs are transported into the cell wall. It was found that mosses with higher concentrations of red pigments and UVACs located in the cell walls, rather than intracellularly, performed better in higher intensity light. Color change in the mosses was found not to be due to chloroplast movement within the cell. It was found that UVACs and red pigments function as long-term photoprotection in Antarctic mosses. Therefore, in response to high-intensity light stress, the production of UVACs and red pigmentation is up-regulated.[10]
Knowing that plants are able to differentially respond to varying concentrations and intensities of light, it is essential to understand why these reactions are important. Due to a steady rise in global temperatures in recent years, many plants have become more susceptible to light damage. Many factors including soil nutrient richness, ambient temperature fluctuation and water availability all impact the photoprotection process in plants. Plants exposed to high light intensity coupled with water deficits displayed a significantly inhibited photoprotection response.[11] Although not yet fully understood, photoprotection is an essential function of plants.
In humans
[edit]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.[12] 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. [13] This means that less than 0.1% of the excited melanin molecules will undergo harmful chemical reactions or produce free radicals.
Synthetic Melanocyte-stimulating hormone
[edit]In the European Union and United States, afamelanotide is indicated for the prevention of phototoxicity in adults with erythropoietic protoporphyria.[14][15][16] Afamelanotide is also being investigated as a method of photoprotection from in the treatment of polymorphous light eruption, actinic keratosis and squamous cell carcinoma (a form of skin cancer).[17]
Artificial melanin
[edit]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.[18] In fact, the substances used in sunscreens are often used as photosensitizers in chemical reactions. (see Benzophenone).
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.[19][20]
| UV-absorber | other names | percentage of molecules that dissipate the photon energy (quantum yield: Φ ) [18] |
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
[edit]References
[edit]- ^ Bailey S, Grossman A (2008). "Photoprotection in cyanobacteria: regulation of light harvesting". Photochemistry and Photobiology. 84 (6): 1410–20. doi:10.1111/j.1751-1097.2008.00453.x. PMID 19067963. S2CID 8432700.
- ^ Kirilovsky D, Kerfeld CA (July 2013). "The Orange Carotenoid Protein: a blue-green light photoactive protein". Photochemical & Photobiological Sciences. 12 (7): 1135–43. doi:10.1039/C3PP25406B. PMID 23396391.
- ^ Berera R, van Stokkum IH, d'Haene S, Kennis JT, van Grondelle R, Dekker JP (March 2009). "A mechanism of energy dissipation in cyanobacteria". Biophysical Journal. 96 (6): 2261–7. Bibcode:2009BpJ....96.2261B. doi:10.1016/j.bpj.2008.12.3905. PMC 2717300. PMID 19289052.
- ^ Dong C, Tang A, Zhao J, Mullineaux CW, Shen G, Bryant DA (September 2009). "ApcD is necessary for efficient energy transfer from phycobilisomes to photosystem I and helps to prevent photoinhibition in the cyanobacterium Synechococcus sp. PCC 7002". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1787 (9): 1122–8. doi:10.1016/j.bbabio.2009.04.007. PMID 19397890.
- ^ Allahverdiyeva Y, Mustila H, Ermakova M, Bersanini L, Richaud P, Ajlani G, Battchikova N, Cournac L, Aro EM (March 2013). "Flavodiiron proteins Flv1 and Flv3 enable cyanobacterial growth and photosynthesis under fluctuating light". Proceedings of the National Academy of Sciences of the United States of America. 110 (10): 4111–6. Bibcode:2013PNAS..110.4111A. doi:10.1073/pnas.1221194110. PMC 3593875. PMID 23431195.
- ^ Tchernov D, Silverman J, Luz B, Reinhold L, Kaplan A (2003). "Massive light-dependent cycling of inorganic carbon between oxygenic photosynthetic microorganisms and their surroundings". Photosynthesis Research. 77 (2–3): 95–103. doi:10.1023/A:1025869600935. PMID 16228368. S2CID 21353640.
- ^ Galvão VC, Fankhauser C (октябрь 2015 г.). «Ощущение световой среды в растениях: фоторецепторы и ранние шаги сигнализации» (PDF) . Современное мнение о нейробиологии . 34 : 46–53. doi : 10.1016/j.conb.2015.01.013 . PMID 25638281 . S2CID 12390801 .
- ^ Zheng XT, Chen YL, Zhang XH, Cai ML, Yu ZC, Peng Cl (апрель 2019 г.). «Арабидопсис с дефицитом ANS чувствителен к высоким светом из-за нарушения фотозащиты от антоциана». Функциональная биология растений . 46 (8): 756–765. doi : 10.1071/fp19042 . PMID 31023420 .
- ^ Takshak S, Agrawal SB (апрель 2019 г.). «Оборонный потенциал вторичных метаболитов в лекарственных растениях при УФ-стрессе». Журнал фотохимии и фотобиологии B: Биология . 193 : 51–88. doi : 10.1016/j.jphotobiol.2019.02.002 . PMID 30818154 .
- ^ Подпрыгнуть до: а беременный Waterman MJ, Bramley-Alves J, Miller RE, Keller PA, Robinson SA (ноябрь 2018 г.). «Передовисть, усиленная пигментами красной клеточной стенки в трех восточных антарктических мохах» . Биологические исследования . 51 (1): 49. DOI : 10.1186/S40659-018-0196-1 . PMC 6247747 . PMID 30463628 .
- ^ Munné-Bosch S, Cela J (декабрь 2006 г.). «Влияние дефицита воды на фотохимию фотохимии Photogystem II во время акклиматизации мудреца Lyreleaf (Salvia Lyrata L.) растений под высоким светом». Журнал фотохимии и фотобиологии B: Биология . 85 (3): 191–7. doi : 10.1016/j.jphotobiol.2006.07.007 . PMID 16962788 .
- ^ Колер Б. "Сверхбывающее внутреннее преобразование ДНК" . Кафедра химии, Университет штата Огайо . Архивировано из оригинала 20 июля 2011 года . Получено 2008-02-13 .
- ^ Мередит П., Риз Дж (февраль 2004 г.). «Радиационная релаксация квантов для синтетического эймеланина». Фотохимия и фотобиология . 79 (2): 211–6. arxiv : cond-mat/0312277 . doi : 10.1111/j.1751-1097.2004.tb00012.x . PMID 15068035 . S2CID 222101966 .
- ^ Комиссар, Управление (24 марта 2020 г.). «FDA одобряет первое лечение, чтобы увеличить безболезненное воздействие света у пациентов с редким расстройством» . FDA . Получено 2024-04-24 .
- ^ «Scenese: краткое изложение характеристик продукта» (PDF) . Европейское агентство по лекарственным средствам (EMA). 27 января 2016 года. Архивировал (PDF) из оригинала 6 апреля 2017 года . Получено 6 апреля 2017 года .
- ^ "Scenese Epar" . Европейское агентство по лекарственным средствам (EMA) . 17 сентября 2018 года. Архивировано с оригинала 19 ноября 2019 года . Получено 18 ноября 2019 года .
- ^ Clinuvel Faqs Archived 2008-04-11 на машине Wayback
- ^ Подпрыгнуть до: а беременный Cantrell A, McGarvey DJ, Truscott TG (2001). «Глава 26: Фотохимические и фотофизические свойства солнцезащитных кремов». В Giacomoni Pu (ред.). Комплексные серии в фотосессиях . Тол. 3. С. 497–519. doi : 10.1016/s1568-461x (01) 80061-2 . ISBN 9780444508393 Полем CAN 137: 43484.
- ^ Burnett Me, Wang SQ (апрель 2011 г.). «Текущие споры солнцезащитного крема: критический обзор». Фотодерматология, фотоиммунология и фотомелия . 27 (2): 58–67. doi : 10.1111/j.1600-0781.2011.00557.x . PMID 21392107 .
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