Phylogenetic Variations in the Calcium-Dependent Electrophoretic Shift of α-Lactalbumin

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Abstract
.alpha.-Lactalbumin undergoes a calcium-dependent electrophoretic shift at pH 8.3. When Ca2+ is removed by a chelator, the mobility of the protein increases, reflecting the exposure of negative electrical charges. The shift, however, is not observed by electrophoresis in the presence of SDS, which demonstrates that .alpha.-lactalbumin does not undergo a measurable conformational change upon debinding of Ca2+. Relative electrophoretic mobilities vary from 1.0 (no shift) to 1.4 among .alpha.-lactalbumins of different orders of mammals. The differences suggest a variable number of gram atoms of Ca2+ bound to .alpha.-lactalbumin or substitution of amino acid Ca2+ ligands in the calcium-binding loop.