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

US Department of Agriculture, Eastern Regional Research Center, Philadelphia, PA 19118

Robert Jenness

Primate Research Institute, New Mexico State University, Holloman Air Force Base, NM 88330

Claire E. Kotts

Monsanto Company, St Louis, MO 63198

ABSTRACT

a-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 -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 -lactalbumins of different orders of mammals. The differences suggest a variable number of gram atoms of Ca²⁺ bound to -lactalbumin or substitution of amino acid Ca²⁺ ligands in the calcium-binding loop.