Ultra-Efficient Hemoglobin Key To Evolutionary Success Of Fish

Brett Smith for redOrbit.com – Your Universe Online

The primordial oceans in Earth´s early days were a much more inhospitable than they are today, and new research published in the journal Science suggests that fish developed a highly efficient hemoglobin-based system to deliver large amount of oxygen to their tissues.

“Four hundred million years ago the oceans were not what they are today. They were low in oxygen, high in CO2 and acidic,” said study co-author Jodie Rummer of the Australian Research Council´s Centre of Excellence for Coral Reef Studies.

“Yet the fishes not only survived in these unpromising circumstances, they managed to thrive,” she continued. “Their secret weapon was a system for unloading huge amounts of oxygen from the hemoglobin in their blood, whenever the going got really tough.”

Hemoglobin, an iron-rich blood protein, carries oxygen to the brain, heart and other organs of all vertebrates. As the evolutionary precursors to land animals, these early fish most likely passed on their use of hemoglobin to humans.

“Hemoglobin in the blood takes up oxygen in the gills of fish and the lungs of humans,” Rummer said. “It then carries it round the body to the heart, muscles and organs until it encounters tissues that are highly active and producing a lot of CO2.”

“The acid is a signal to the hemoglobin to unload as much of its oxygen as possible into the tissues,” she explained.

“These early fish managed to develop a way to maximize the delivery of oxygen, even when the water they lived in was low in it,” Rummer added. “They had a phenomenal capacity for releasing oxygen just when needed: it was one of the big secrets of their evolutionary success, to the extent they now make up half the vertebrates on the planet.”

Rummer and a team of international colleagues discovered the hemoglobin system by analyzing the biochemistry of rainbow trout, which are capable of rapidly doubling oxygen release for certain tissues during stressful situations.

This oxygen release system has become very efficient over the past 150 to 270 million years, the researchers said. It is able to deliver large quantities of oxygen to organs such as the eye, an essential organ for clearly spotting underwater predators or prey.

The fish hemoglobin system is probably more efficient than ours because our amphibian ancestors branched away from more evolved fish about 350 to 400 million years ago when the oxygen-delivering method was still in its early stages of development, the researchers said in a statement.

The study authors said their findings could lead to new ways of studying oxygen conditions in the body.

“Also, we feel that if we can understand how fish coped with low-oxygen, high CO2, acidic waters in the past, it will give us some insight into how they might cope with man-made climate change which appears to be giving rise to such conditions again,” Rummer said.

Hemoglobin is also capable of carrying other gases in the blood stream, including carbon dioxide. The protein is also found outside of red blood cells where it can act as an antioxidant.

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