BETA-LACTOGLOBULIN

Information of the bioactivity of beta-lactoglobullin is somewhat limited. Most of the information on beta-lactoglobulin in the past several years relates to the activities of the peptides derived from it by digestion. See Peptides.

b-lactoglobulin is the major protein in whey, making up about 50- 60% of the total protein. It exists in milk as a dimer in solution because of electrostatic interaction of Asp¹³⁰ and Glu¹³⁴ of one monomer with corresponding lysine residues of another monomer. The conformation of the protein is pH dependent and heat sensitive. At low temperature (2 ^oC) and between pH 3.7 and 5.1, the dimer self-associates into an octomer form. The role, if any, of the various quaternary forms of b-lactoglobulin to biological function is not known.

The characteristics and functionality of b-lactoglobulin have been extensively reviewed. These include reviews by Morr and Ha, 1993; Kinsella and Whitehead. 1989; Leman and Kinsella, 1989; Modler and Jones, 1987; McDermott, 1987: Nakai and Chan, 1985; and Morr, 1985.

Recent reports by Maubois etal. (1995) and Burr, etal (1996) have suggested that the heat treatment of milk can cause the formation of lactosylated b-lactoglobulin that is covalently bound through lysine as a result of Maillard reaction. Up to 4 lactose molecules have been shown to be present, covalently bound to one molecule of b-lactoglobulin (Burr, etal., 1996).

Glycosylation of b-lactoglobulin has been shown to alter the conformation of the protein, resulting in a reduced net charge, increased relative viscosity and a decrease in the a-helical content (Kinsella and Whitehead, 1989, Waniska and Kinsella, 1988) The effect of glycosylation on its biological functionality is not known at this time

Biological activity:

A biological function for beta-lactoglobulin has been the subject of much speculation, but no specific function has been proven. It does bind retinol and has been considered as a possible transport protein for retinol (Hambling, etal., 1992).

There is a possibility that lactosylation of b-lactoglobulin can alter its biological activity. This is supported by Shida, etal. (1994), who recovered two proteins from the proteose peptone fraction of heated milk that could bind E. Coli enterotoxin, but not cholera toxin. The products had molecular weight of 15,500 and 20,000 and where identical to beta-lactoglobulin and alpha-lactalbumin based on immunoblot and amino acid sequence. The anti-toxin activity was reported to be lost when the products were treated with b-galactosidase.

Acylation, succinylation, or aconnitrylation of b-lactoglobulin resulted in products that had strong antiviral activity against human immunodeficiency virus types 1 and 2.