The evolution of lysozyme and α‐lactalbumin

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. Copyright © 1989, Wiley Blackwell. All rights reserved