( K. H. Valkonen* N. Mart...)Purification and Characterization of beta-Lactoglobulin Genetic Variants A and B Using Preparative Electrophoresis and Isoelectric Focusing

K. H. Valkonen*, N. Marttinen*, H.-L. Malinen*, V.-P. Jaakola** and T. Alatossava*

* Biotechnology Laboratory, REDEC of Kajaani, University of Oulu, FIN-88600 Sotkamo, Finland
** Department of Biological and Environmental Science, University of Jyvskyl, PL 35, FIN-40351 Jyvskyl, Finland

Introduction
β-lactoglobulin (βLG) is a major whey protein found in the milk of cows and other ruminants, deer, bison, and buffalo. βLG is also found in some nonruminants, such as pigs,¹ horses,² dogs, dolphins,³ cats,⁴ and whales. However, βLG is not found in human milk.^{5, 6, 7, 8} βLG is a glycoprotein which exists at the normal pH of bovine milk as a dimer with a molecular weight of 36,000, and consists of two monomeric subunits with molecular weight of 18,000 (162 residues). Several genetic variants of βLG have been detected,⁹ of which the bovine phenotype A and phenotype B are most predominant. The bovine βLG A variant differs from the βLG B variant by only two amino acids: aspartate-64 (Asp) and valine-118 (Val). These amino acids are substituted by glycine (Gly) and alanine (Ala) in the B variant. All variants contain five cysteine residues, four of which are involved in forming intrachain disulfide bridges.

The function of βLG is not yet clear, although binding and transport of retinol, small hydrophobic ligands and fatty acid in postnatal animals, have been suggested as possible functions, since its three-dimensional structure is essentially similar to that of human retinol-binding protein in serum.^{10, 11, 12, 13, 14, 15} βLG
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