Photoprotective Substances

For all phototrophic organisms exposed to UV radiation for substantial parts of their life cycles, strategies that passively screen UV radiation will contribute to preventing UV-induced direct and indirect damage to essential biomolecules. In addition, UV-screening may also save metabolic energy by reducing the need for constantly active avoidance and repair processes. 

The most common photoprotective sunscreens in many, but not all algal taxa and cyanobacteria are the mycosporine-like amino acids (MAAs), a suite of chemically closely related, colourless, water-soluble, polar and at cellular pH uncharged or zwitterionic amino acid derivatives (Fig. 13.4). 

The function of MAAs as intracellular screening agents has been inferred in numerous red algae from a decrease in concentration with increasing depth (Hoyer et al. 2001,2003). Supra- and eulittoral red algal species typically experience 

Based on the MAA concentrations and the induction patterns after exposure to different radiation conditions red algae can be physiologically classified in three categories (Hoyer etal. 2001) Type / - no MAAs at all Type II - MAAs inducible 

Besides the stimulating effect of increasing solar radiation on the biosynthesis and accumulation of MAAs in many algae and cyanobacteria, other environmental factors may also influence them. Nutrient availability (e.g. ammonia) in particular has positive effects on MAA concentrations (Korbee et al. 2005). 

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Hoyer K, Karsten U, Sawall T, Wiencke C (2001) Photoprotective substances in Antarctic macroalgae and their variation with respect to depth distribution, different tissues and developmental stages. MarEcol Prog Ser211 117-129... 

D.L. Fabacher, E.E. Little (1998). Photoprotective substance occurs primarily in outer layers of fish skin. Environ. Sci. Poll. Res., 5,4-6. 

Table 1. Absorption maximum (A ax) amount of photoprotective substance in methanol extracts of various tissues from rainbow trout Oncorhychus mykiss) and razorback suckers Xyrauchen texanus). [from Fabacher and Little 68]...

Figure 5. Spectrophotometric UV absorbance of photoprotective substance from the skin of razorback sucker Xyrauchen texanus). Absorbance maximum occurs at 294 nm, the broad shoulders of the absorbance curve would provide protection from UV wavelengths less than and greater than 294 nm. [From Fabacher and Little 68.]...

Several other UV-absorbing compounds have been described as potential photoprotectants in cyanobacteria and algae, but these substances are not as common as MAAs or scytonemin. 

A study on the photoprotective effect of the topical application of 2% vitamin E and 5% vitamin C in humans showed no effect with the application of each substance alone, but an enhanced photo-protective effect after applying vitamins E and C combined, which was attributed to the regeneration of vitamin E by vitamin C.20 This enhanced effect has also been shown with the topical application of a combination of 15% ascorbic acid and 1% a-tocopherol to porcine skin.21 The combined systemic supplementation of vitamins C and E was similarly able to reduce sunburn reactions22 and to increase the minimal erythema dose (MED), a measure for individual photosensitivity, more than supplementation with either vitamin E or vitamin C alone.23,24 An oral supplementation with an anti-oxidative combination of carotenoids (P-carotene and lycopene), vitamin C, vitamin E, selenium, and proanthocyanidins (Seresis , Pharmaton SA, Lugano, Switzerland) also reduced the development and grade of UVB-induced erythema 25... 

Photoprotection is a group of mechanisms that nature has developed to minimize the damages that an organism encounters, when exposed to UV radiation (UVR). These mechanisms can be controlled or organized by certain organic and inorganic compounds or substances (e.g., melanin)... 

The same transformation was subsequently conducted in vitro from substances isolated from Tridachiella diomedea and Tridachia crispata (Ireland and Faulkner, 1981). Thus, several polypropionates, such as cyercene, pladdene and deoxytridachione, that undergo in vivo photoisomerization may have a role in photoprotection (Zuidema and Jones, 2005). 

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