bio

Myoglobin

The oxygen-holding protein inside muscle cells, distinct from the haemoglobin that carries oxygen in blood. Myoglobin is each muscle's private air tank, drawn on once the blood has been clamped off and no longer arrives. Human muscle holds 4–7 mg per gram; the muscle of deep-diving marine mammals holds 50–80 mg, dark enough to look almost like ink. Packing protein that densely should make it clump and precipitate; Mirceta and colleagues (2013) found that diving lineages independently evolved the same fix — swapping surface residues for positively charged ones, so the molecules repel each other and never stick.