133: Zinc-based sulfide-binding mechanism in tubeworms
The unusual form of hemoglobin gives the worms an advantage over other organisms competing for space near the vents and may play a role in their ability to adapt to a wide temperature range.The tubeworms, which grow in the bizarre deep-sea vent environment, have a highly efficient hemoglobin, which carries both sulfide and oxygen. They do this by modifying the hemoglobin proteins into a more stable form than the human version, and integrating zinc to increase the binding points for sulfide and oxygen.
Why not use an entirely new molecule? Because evolution works with what's there. Why don't we have this super-efficient hemoglobin? Perhaps because too much oxygen is a bad thing.