A reader draws our attention to Prof. Eric Arnoy’s comments at Calvin College, BiochemistryII:
The reduction of nitrogen to ammonia, known as nitrogen fixing, is vital to agriculture:
N2 + 3H2 → 2NH3
The bacteria that perform this job for plants are symbionts with th plants, exchanging ammonia for energy. The plant provides leghemoglobin to bind the oxygen.
Now, here’s the interesting part: Leghemoglobin is part of the globin protein family and resembles the mammalian oxygen-binding protein myoglobin in structure, though the sequences differ greatly. But how is that? Arnoy writes,
Furthermore, myoglobin is not found in plants, so it would be a stretch to suggest that leghemoglobin arose from myoglobin. Instead, what we see here is a wonderful example of convergent evolution in which the optimum oxygen-binding structure is found in two very different types of organisms. More.
See also: Venom in fish evolved 18 times
and
“Spectacular” convergence between ancient mammal and dinosaur
Evolution appears to converge on goals—but in Darwinian terms, is that possible?
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