Charge changes in protein evolution.

The number of charge changes relative to total amino acid replacements for each of seven protein sequences (cytochrome c, hemoglobin alpha, hemoglobin beta, myoglobin, insulin, and fibrinopeptides A and B) has been studied. This number was compared with the expected value obtained under the assumption of random nucleotide substitution. The results obtained indicate that four proteins--hemoglobin alpha, hemoglobin beta, myoglobin, and insulin--are accumulating charge changes at rates slower than those predicted by a model of random substitution. Cytochrome c and fibrinopeptides A and B are accumulating charge changes at rates similar to those predicted by a random model.