The Primary Structure of Donkey(Equus asinus)Lysozyme contains the Ca(II) Binding Site of α-Lactalbumin

The complete primary structure of donkey lysozyme has been established by pulsed liquid-phase sequencing of tryptic and chymotryptic peptides isolated by RP-HPLC. The positions of the Cys residues were identified by labeling the Cys residues with DABIA-reagent. Donkey lysozyme is a c-type lysozyme which is 129 amino acids long. It exhibits 50% homology to the human protein. We observe the full Ca(II) binding site suggested for the homologous alpha-lactalbumines. Although horse lysozyme has been reported to contain asparagine in position 61, which was in conflict with the three-dimensional structure of lysozyme, all other known c-type lysozymes, including donkey, contain Ser 61.