Department of Polymer Science, Faculty of Science, Hokkaido University, Japan.
It was found that pigeon lysozyme binds one calcium ion, as does equine lysozyme. The protein was eluted with equimolar calcium ions from a Bio-Gel P-60 column. The binding constants of equine and pigeon lysozymes were determined to be 2 x 10(6) and 1.6 x 10(7) M-1, respectively, in 0.1 M KCl at pH 7.1 and 20 degrees C. During evolution the gene of calcium-binding lysozyme is deduced to be separated from that of non-calcium-binding lysozyme by gene duplication before splitting of avian and mammalian lineages, from their amino-acid sequences. It is assumed that the alpha-lactalbumin might have evolved from calcium-binding lysozyme.