Evolutionary Rate and Role of Selection

TABLE 18.2 Frequencies of occurrence and relative variabilities of amino acids in proteins 

Amino acid residues Frequencies in proteins (%) Variability/ Mutability 

Notes 1. Frequencies of occurrence of amino acid residues in 1021 unrelated proteins, taken from McCalden and Argos (1988). 

Variability expresses the number of times that a given amino acid residue has changed during the evolution of various homologous proteins divided by the number of times the residue occurred. The values have been normalized (highest value to 100), taken form Dayhoff (1978). 

Notes 1. One PAM (Point acc ted mutation) is a unit of evolutionary diva-gence in which 1% of the amino acids have 

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