Primary structure of water buffalo (alpha)-lactalbumin variants A and B

A novel electrophoretic (alpha)-lactalbumin ((alpha)-la) variant was detected in the Italian water buffalo breed. The isoelectric point of the variant, labelled A, was lower than the most frequent variant B. It presented an allelic frequency of 0u5% compared with the 97u1% of the BB allele. From Liquid Chromatography-Electrospray Ionization/Mass spectrometry, the molecular mass of the two (alpha)-la A and B variants were measured as 14235u1+-0u8 and 14236u1+-0u9 Da, respectively. The two proteins were sequenced and differentiated from one another by a single amino acid substitution, Asn^45(B)(rightward arrow)Asp^45(A). As this amino acid substitution altered the N-glycosylation sequence consensus Asn45-X-Ser^46 it may be deduced that the protein glycosylation level of the (alpha)-la A would decrease.