The Ohio State University study revealed how the enzyme photolyase uses energy from visible light to repair UV damage.

This enzyme is missing in all mammals, including humans, although all plants and all other animals have it. Greater understanding of how photolyase works could one day lead to drugs that help repair UV damage in human DNA.

In the online edition of the Proceedings of the National Academy of Sciences, Dongping Zhong and his colleagues report experimental evidence of what scientists have long suspected -- that visible light excites the photolyase molecule and boosts the energy of electrons in its atoms. This in turn enables the enzyme to inject an electron into the DNA molecule at the UV damage site temporarily to perform repairs.

They also report something that was unexpected: Water plays a key role in the process, by regulating how long the donated electron stays inside the damage site before returning to the photolyase molecule.

Scientists believe that all placental mammals lost the ability to make this enzyme some 170 million years ago, said Zhong, an assistant professor of physics and adjunct assistant professor of chemistry and biochemistry at Ohio State.

That's why humans, mice, and all other mammals are particularly vulnerable to cancer-causing UV rays from the sun. But the rest of the animal kingdom insects, fish, birds, amphibians, marsupials, and even bacteria, viruses and yeast retained a greater ability to repair such damage.

Since the 1940s, scientists have been trying to understand how the DNA in plants and some animals can be damaged by UV light, and then seemingly repaired by visible light. In the 1960s, they identified the enzyme that was responsible for the repair, and named it photolyase, but they didn't know exac
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Contact: Dongping Zhong
Zhong.28@osu.edu
614-292-3044
Ohio State University
12-Sep-2005