Multiple Forms ofβ2-Microglobulin in Human Colostrum

Abstract

Purification of β₂-microglobulin from human colostrum was performed by removal of fat by centrifugation and of casein by acid precipitation, followed by gel filtration and ion exchange chromatography of the whey. The β₂-microglobulin was isolated in two peaks by Sephadex G–75 column chromatography. The high molecular weight fraction had the molecular weight of 48,000 which is the same as that of lactollin, a tetrameric form of β₂-microglobulin. The other fraction of β₂-microglobulin showed three bands on disc gel electrophoresis at pH 8.5 and all of them were able to react with the antiserum of β₂-microglobulin. They were not separated each other by gel filtration and ion exchange chromatography and apparently had the same molecular weight of 12,000. However, they migrated as a single band in disc gel electrophoresis at pH 4.3 and it was concluded that these three bands at pH 8.5 were charge isomers.