Identification and the Primary Structure of Equine α-Lactalbumin B and C(Equus caballus,Perissodactyla)

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Abstract
The presence of two new .alpha.-lactalbumins has been demonstrated in the colostrum of a single mare (Equus caballus, Persian Arab). They have been designated equine .alpha.-lactalbumin B and C, and that isolated previously from the milk of Australian horses (English Thoroughbred) as .alpha.-lactalbumin A. The primary structures of B/C have been determined by automatic Edman degradation of enzymatic cleavage of the oxidized protein. Cyanogen bromide cleavage of S-carbamoyl-methylated protein provided necessary overlapping peptides. Comparison of the sequences of B and C with that of A indicates 3 and 4 amino-acid exchanges, respectively. The phylogenetic difference of equine .alpha.-lactalbumin B/C from bovine .alpha.-lactalbumin B is indicated by 39 and 40 amino-acid exchanges, respectively. The structure-function relationship, calcium binding sites and variants of .alpha.-lactalbumin are discussed.