Multiple Forms of β2-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.