EVIDENCE OF MULTIPLE GLYCOSYLATION OF BOVINE BETA-LACTOGLOBULIN BY ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY

Electrospray ionisation mass spectrometry (ESI-MS) was used in the cha racterisation of beta-lactoglobulin (beta-LG) A, B and C variants puri fied from the milks of 109 individual cows. Capillary electrophoresis and reverse phase-HPLC were used to confirm the purity of the samples, which contained either 1 species in the case of samples prepared from cows homozygous for a particular beta-LG variant or 2 species in the case of samples prepared from cows heterozygous for this protein. Howe ver, all samples were found to contain multiple molecular weight speci es of beta-LG when analysed by ESI-MS. In addition to spectral peaks c orresponding to the known molecular masses of the A, B and C variants, peaks were observed which differed in molecular weight from beta-LG b y increments of approximately 324 mass units. Although less marked, th e +324 Da molecular weight species were also present in a sample of be ta-LG purchased from the Sigma Chemical Company.