Anti-freeze fish

On its face, it may seem like a silly question: why don't fish freeze in freezing water?

Humans living in cold climates have long known that Antarctic fish can survive at temperatures where they should normally freeze to death. Fish blood freezes at -0.9 degrees Celsius, but Antarctic waters are over a degree colder than that. Scientists have known for many years that a protein carried by the bloodstream stops the fish blood from freezing, but they just didn't know exactly how it worked.

In a bid to solve this problem, scientists at the University of Illinois extracted the protein from a fish called an Antarctic hake and enlisted the help of Martina Havenith, a chemistry professor at Ruhr University in Bochum, to figure out how the proteins stop the water in fish blood from freezing.

Their results were published last month in the Journal of the American Chemical Society.

Using radiation to detect water movement

Havenith and her team built what they say is the most powerful tabletop terahertz spectrometer in the world.

"Until now, scientists didn't have anything suitable to measure the effect that proteins have on water," she said in an interview with Deutsche Welle.

"It's like when a photographer takes a picture and the exposure's too long, he can't see what's happening. But with terahertz, the exposure is just right and it can measure this relationship between the proteins and the water for the first time."

Terahertz radiation is a low-frequency radiation just beyond the microwave band and just before the infrared band. Scientists say that it turns out that this frequency is excellent at probing proteins and water.

"What we find out is that the terahertz region is very sensitive to any changes in the rearrangement or restructuring of water," said Havenith.

The spectrometer emits a laser, and when the laser hits pure water, it absorbs radiation. When the anti-freeze protein is added, the water starts moving in a different way and more radiation is absorbed. A receptor picks up these minute changes in radiation, and from the data, Havenith can figure out how the water molecules are moving.

From disco dancing to square dancing

In normal conditions, water molecules are constantly moving around, repeatedly making new bonds amongst themselves.

When the anti-freeze proteins are added, the water molecules couple and decouple with the proteins trillions of times every second. As they interact, the protein changes the water and the water molecules start to move in a slower, more orderly fashion.

Martina Havenith compares the change in movement to an orderly square dance.

"The proteins are always opening and closing," she said. "The water doesn't bind with the proteins. They're constantly changing partners, like in a disco dance. When the protein interacts with the water, it changes the properties of the water, so that the dance becomes more ordered. The disco-dance becomes a square dance."

The research showed that a single protein molecule can affect the behavior of 1,000 water molecules around it. Further, the anti-freeze protein tends to work better at temperatures closer to zero degrees Celsius.

"The anti-freeze protein prevents freezing several hundred times better than any anti-freeze you put into your car," Havenith added.

Future applications for organ donation

The German-American team of scientists sees great potential for using the anti-freeze proteins to preserve transplanted organs for longer.

When a transplant organ becomes available, it's a race against time to find a suitable recipient who isn't too far away. A heart that's laced with preservatives and placed on ice can only survive outside a body for around five hours. So if a recipient isn't found in time or they live too far away, the organ can't be used.

Havenith and Gruebele both think that the proteins could be used to store organs at colder temperatures without freezing them, which can damage the organ tissue.

"If we could better understand how these proteins work, maybe we can copy the properties that make them work, or design human versions," said Martin Gruebele, a chemistry professor at the University of Illinois and co-author on the study. "We could then preserve transplant organs longer or design frostbite protection."

The team intends to use the terahertz spectrometer to study anti-freeze proteins from insects and other kinds of proteins.

Research has promise

Other biochemists say that this research has a lot of potential for future study and perhaps even commercial applications.

"It's certainly a very interesting discovery," said David Nutt, a chemistry professor at Reading University in the United Kingdom, who was not part of the study.

"It's another piece in the puzzle and I'm looking forward to what comes out of her group next," he added. "There are certainly a lot of interesting proteins to look at using this technique and I'm sure there'll be lots of interesting results in the future."

He noted that terahertz spectrometry only provides part of the picture, and that the research needed to be confirmed through further examination that could yield more precise information on the exact motion of frozen water molecules.

"I think the spectrometry needs to be supplemented by computer modeling and other forms of experiments in order to actually work out what these results mean," he said.

Author: Natalia Dannenberg
Editor: Cyrus Farivar