Seals, dolphins, whales and other mammalian marine animals have evolved the ability to hold their breaths underwater for extended periods. Scientists have long been interested in how they achieve these underwater feats of endurance. In an article in Science this week a group from Liverpool University has proposed a molecular mechanism that accounts for this ability.
Oxygen is stored in muscles using a protein called myoglobin. Like most proteins you can only have myoglobin at certain concentrations because proteins in high concentration tend to form dysfunctional aggregates. This means that for you or I there is a theoretical maximum amount of oxygen our muscles can store.
So how do marine mammals manage to get around this? Simple, they have a mechanism that allows them to pack more myoglobin together without it forming aggregates. Proteins are made up of amino acids, there are 22 standard amino acids some of which have either a positive or negative charge. If the protein evolves enough of these charged amino acids on its surface it will have a high net electro-static charge and it will repel other copies of itself just like trying to bring together the negative poles of two magnets.
This is exactly what has happened to myoglobin as it has evolved in marine mammals. It’s gained a high electrostatic charge which means molecules of myoglobin repel each other and this in turn prevents aggregation.
This means that marine mammals can pack together far more myoglobin molecules and their muscles can hold far more oxygen allowing them to dive for much longer between breaths.