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WASHINGTON http://www.cheapestairmaxfromchina.com/ , Feb. 19 (Xinhua) -- Much of the damage that ultraviolet radiation (UV) does to skin occurs hours after sun exposure, and this delayed reaction appears to be due to the skin pigment melanin, a U.S. study said Thursday.
Melanin, which gives skin its color, is usually thought of as a protective pigment cheap air max tn , blocking the UV radiation that damages DNA and contributes to skin cancer.
But there was also evidence from studies suggesting that melanin was associated with skin cell damage.
In the new study, Douglas Brash, professor of the Yale University, and his colleagues first exposed mouse and human melanocytes, the cells that make the melanin cheap air max 270 , to radiation from a UV lamp.
The radiation caused a type of DNA damage known as a cyclobutane dimer (CPD), in which two DNA "letters" attach and bend the DNA, preventing the information it contains from being read correctly.
The researchers were surprised to find that the melanocytes not only generated CPDs immediately but continued to do so more than three hours after UV exposure ended. Cells without melanin generated CPDs only during the UV exposure.
The results, published in the U.S. journal Science, showed that melanin had both carcinogenic and protective effects.
"If you look inside adult skin cheap air max 95 , melanin does protect against CPDs. It does act as a shield," said Brash. "But it is doing both good and bad things."
The researchers next tested the extent of damage that occurred after sun exposure by preventing normal DNA repair in mouse samples. They found that half of the CPDs in melanocytes were " dark CPDs" -- CPDs created in the dark.
Further research showed that the UV light activated two enzymes that combined to "excite" an electron in melanin, and that the energy generated from this process, known as chemiexcitation, in turn cheap air max 97 , causes the same DNA damage that sunlight caused in daytime.
Chemiexcitation has previously been seen only in lower plants and animals.
While noting that news of the carcinogenic effect of melanin is disconcerting, the researchers also said that the slowness of chemiexcitation may allow time for new preventive tools, such as an "evening-after" sunscreen designed to block the energy transfer.
SAO TOME, Jan. 17 (Xinhua) -- Chinese Foreign Minister Wang Yi here on Tuesday called on African countries not to miss China-Africa cooperation opportunities.
At a press conference in Sao Tome and Principe, Wang said he hoped Sino-African cooperation will not omit any African country.
Wang was in Sao Tome and Principe Tuesday in the last leg of his new year African trip. Sao Tome and Principe resumed its diplomatic relations with China about a year ago after cutting "diplomatic ties" with Taiwan.
While emphasizing there is only one China in the world and Taiwan is an integral part of the Chinese territory cheap air max 90 , Wang hailed Sao Tome and Principe's right decision to restore diplomatic relations with China.