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A beach holiday often involves sunbathing on a hot beach before trying to avoid getting stung by jellyfish while swimming in the sea. Now, it appears there might be even more reason to avoid jellyfish, because Chinese food scientists have discovered that peptides extracted from jellyfish can inhibit the tanning process. But what is bad news for sun worshippers could be good news for those suffering from skin blemishes and for farmers trying to grow bruise-free produce. A nice all-over tan is the result of special cells in the skin called melanocytes producing a pigment known as melanin, which is also found in the eyes and hair. This process is known as melanogenesis and involves an enzyme called tyrosinase converting the amino acid tyrosine into melanin via a sequence of oxidation reactions. As with many biological processes, melanogenesis can sometimes go slightly awry. This can lead to an over- or under-abundance of melanin in certain areas of the skin, with an over-abundance producing skin blemishes such as chloasma (dark, irregular skin patches), age spots and freckles. Melanogenesis also causes the unattractive bruising than can occur on fresh fruit and vegetables. So both cosmetic companies and food producers are looking at ways to control melanogenesis. One of the options being explored is inhibiting tyrosinase, thereby blocking the production of melanin. Unfortunately, although a number of compounds are known to inhibit tyrosinase, such as sulfite or kojic acid, they tend to be quite toxic. Recently, however, scientist have discovered that various proteins and peptides extracted from natural sources such as milk, wheat, honey, silk and houseflies are also able to inhibit tyrosinase, especially peptides containing the amino acids arginine and alanine. Collagen is a tough, fibrous protein found in the skin and connective tissues, such as tendons and ligaments, of most animals. Made up of long chains of peptides, collagen is completely non-toxic and is already widely used by industry, including in numerous cosmetics and to produce the gelling agent gelatin. This led a team of food chemists at the Ocean University of China in Qingdao, led by Bafang Li, to wonder whether collagen might make a good and safe source of tyrosinase-inhibiting peptides. Ordinarily, collagen intended for industrial uses is extracted from cows and pigs, which can cause a problem for some people because of religious or ethical concerns. So Li and his colleagues decided to turn to a rather novel source of collagen, which they hoped would cause less ethical problems: jellyfish. Specifically, they extracted collagen from the umbrella of a species of jellyfish known as Rhopilema esculentum, which has been eaten in China for thousands of years. They digested the collagen into its component peptides using the enzyme trypsin and then purified the peptides by passing them through an ion exchange chromatography column and then a gel filtration column. The resultant purified peptides contained high levels of the amino acids glycine, proline and serine, but also contained arginine and alanine. After confirming that the purified peptides showed no toxicity, Li and his team tested their tyrosinase-inhibiting ability on a line of cancer cells. They found that the peptides could indeed inhibit tyrosinase, reducing the synthesis of melanin by up to almost 50%. Investigating further, they discovered that the peptides seem to inhibit tyrosinase in two different but complementary ways: by physically binding with the enzyme and by blocking the oxidation reactions. So it seems that jellyfish may well be both safer and more useful than they first appear when viewed from a hot beach. Related links:
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd. |
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