Purification of bovine beta 2-microglobulin from colostrum and its complete amino acid sequence.

Bovine beta 2-microglobulin (beta 2-m) was purified from colostrum milk in two chromatographic steps: anion-exchange chromatography, and gel filtration. The amino acid sequence was determined to confirm that the purified protein was beta 2-m. A molecular weight of 11.8 kDa beta 2-m was estimated using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Bovine beta 2-m consists of 98 amino acid residues and contains one disulfide linkage connecting residues 25 and 79. The amino acid sequence determined by this study is different from a previously published sequence at three sites, but agrees with the amino acid sequence from cDNA. Thus, we can conclude that the amino acid sequence determined in this study is correct.