Unlike humans, many whales can go on hour-long dives without needing to breathe. But no one has been sure how they did it. Now, new research shows it all comes down to a specially adapted oxygen-binding protein in the animals' muscle tissues — a finding that could someday prove valuable in medicine.
Most mammals, including whales, cows and humans, have a protein in their muscles called myoglobin. The primary job of these molecules is to bind (store) oxygen. So when you exercise, for example, myoglobin provides extra oxygen to your muscles, allowing you to maintain a high level of activity for a long time.
Myoglobin also plays an important role when you hold your breath — though you're not breathing, your body needs oxygen, which myoglobin provides. As you can imagine, animals that can hold their breath for a very long time, such as marine mammals, naturally have a lot more myoglobin in their tissues than we do. Point of fact: Myoglobin gives meat its red color, but the muscles of whales and other diving mammals are black because they have so much of the protein.
It all makes sense on the surface, but one issue lingers: At very high concentrations, proteins are known to clump together, impairing their function. So just how is it that myoglobin, even at disruptively high concentrations, can still store enough oxygen to allow marine mammals to go without breathing for a long time?
By studying the amino-acid sequences of the protein in various animals, including cows, otters (which are semi-aquatic) and sperm whales, researchers found that the myoglobin of diving animals have special non-stick properties.
"Like the similar poles of a magnet; the proteins repel one another," study researcher Michael Berenbrink tells BBC, explaining that the aquatic mammals' myoglobin are more positively charged than those of terrestrial mammals. "In this way we think the animals are able to pack really high concentrations of these proteins into their muscles and avoid them sticking together and clogging up the muscles."
Using this information, the scientists then decided to reconstruct the protein sequences of some of the extinct ancestors of today's diving mammals. Nature explains:
Using the reconstructed sequences from different animals to infer the electric charge on their myoglobin, together with information about the animal’s body mass, the team was able to determine that an early whale ancestor — the terrestrial, wolf-sized animal Pakicetus — couldn’t stay under water for much more than 90 seconds. But the larger, six-tonne Basilosaurus, which appeared about 15 million years later than Pakicetus, could manage about 17 minutes. Many modern whales can remain submerged for more than an hour.
By being able to now predict the maximum dive times of ancient animals, scientists could potentially better understand the ecology and biology of these extinct animals, as well as the evolution of deep diving.
Additionally, understanding how the animals efficiently store oxygen could aid medical research, potentially leading to the development of oxygen-carrying liquids able to deliver oxygen to tissues when blood transfusion is not an option, BBC reports.
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