Characterization of hen egg white- and yolk-riboflavin binding proteins and amino acid sequence of egg white-riboflavin binding protein.

White- and Yolk-riboflavin binding proteins were isolated from hen eggs, and characterized as to their chemical properties. White- and Yolk-RBPs had almost same amino acid compositions except for glutamic acid, but their carbohydrate compositions were different from each other. The complete amino acid sequence of White-RBP was determined by conventional methods. White-RBP comprised 219 amino acid residues, and the amino-terminus was pyroglutamic acid (pyrrolidonecarboxylic acid). Two amino acids, lysine and asparagine, were found at the fourteenth residue from the amino-terminus. Carbohydrate chains were linked to asparagine residues at positions 36 and 147. Both White- and Yolk-RBPs were phosphorylated. In White-RBP either six or seven of nine serine residues between Ser(185) and Ser(197) were phosphorylated. The amino acid sequences around phosphoserines showed that phosphorylation might occur at a serine residue in one of the following sequences; Ser-X-Glu or Ser-X-Ser(P).