Different Proteins Evolve at Very Different Rates

Obviously, we should not rely on a single protein to build an evolutionary tree. If we make trees for several proteins, we often get rather similar evolutionary relationships. However, different proteins evolve at different speeds. As noted above, humans and fish differ by 50% in the a chain of hemoglobin but by less than 20% in their cytochrome c. If we plot the number of amino acid changes versus the evolutionary time scale (Fig. 20.15), we can see this easily for cytochrome c (slow), hemoglobin (both a and b chains evolve at medium speed), and fibrinopeptides A and B (rapid evolution).

Different Proteins Evolve at Very Different Rates 551

FIGURE 20.15 Rates of Protein Evolution

During the course of evolution, some proteins accumulate more mutations than others. The cytochrome c gene is very stable, and only 50 changes/100 amino acids have occurred in 800 million years. Fibrinopeptides A and B, on the other hand, have accumulated 50 changes/100 amino acids in less than 100 million years.

FIGURE 20.15 Rates of Protein Evolution

During the course of evolution, some proteins accumulate more mutations than others. The cytochrome c gene is very stable, and only 50 changes/100 amino acids have occurred in 800 million years. Fibrinopeptides A and B, on the other hand, have accumulated 50 changes/100 amino acids in less than 100 million years.

TABLE 20.05 Rates of Evolution for Different Proteins

Protein

Rate of Evolution

Neurotoxins

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