The evolution of lysozyme and α‐lactalbumin

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Abstract
From the analysis of phylogenetic trees constructed from the amino acid sequences and metal-binding properties of various lysozymes c and α-lactalbumins, it was found that before the divergence of the lineages of birds and mammals, calcium-binding lysozyme diverged from non-calcium-binding lysozyme. α-Lactalbumin evolved from the calcium-binding lysozyme along the mammalian lineage after the divergence of birds and mammals. Rapid evolution took place, not in the process of acquisition of the activity of α-lactalbumin, but after the loss of lysozyme activity, due to the change in the distribution of selective pressure on each amino acid site. A general process for the change in function of a protein during evolution is suggested to be as follows: after duplication of the gene, one of their protein products acquires a new function, besides that already present; the old function is eventually lost.