The whey proteins of ovine milk: β-lactoglobulins A and B

Abstract

It is shown by starch-gel electrophoresis of samples of skim milk from individual ewes that the major part of the whey proteins migrates in three regions at pH 7.6 (phosphate buffer, I 0.2). In the region of highest mobility there is only one band and it represents serum albumin. The second region contains only one band and it corresponds to α-lactalbumin. In the third region there may be one or two bands, each of which is a genetic variant of β-lactoglobulin. These conclusions are confirmed by electrophoretic and immunological studies of total whey protein solutions and fractions isolated therefrom. The faster-moving β-lactoglobulin at pH 7.6 is designated ovine β-lactoglobulin A and the slower one ovine β-lactoglobulin B. Their isolation and properties are described. The A variant can be crystallized readily at pH 5.2. Attempts to crystallize the B variant have failed. Neither variant associates at pH 4.6 and low temperature, thus resembling the bovine B and C variants rather than the bovine A variant. There are marked differences in the ultraviolet spectra due to the difference in tyrosine content. The optical rotatory properties, molecular size and immunological properties are similar to those of the bovine species.