Comparison of the amino acid sequences of hen plasma-, yolk-, and white-riboflavin binding proteins.

The amino acid sequence of hen egg yolk-riboflavin binding protein (yolk-RBP) was determined by conventional methods. The sequence was identical with that of hen egg white-riboflavin binding protein except that their carboxyltermini were different, that of yolk-RBP lacked 11 or 13 amino acid residues, while hen plasma-RBP had the same C-terminal sequence as white-RBP. This indicated that the C-terminal 11 or 13 amino acid residues in plasma-RBP might be cleaved off during the incorporation from the blood into the oocyte or in the yolk fluid. Yolk-RBP had the same characteristics as white-RBP, such as N-terminal pyroglutamic acid, polymorphism in the amino acid sequence (Lys/Asn) at the fourteenth residue from the N-terminal end, carbohydrate chains attached to both Asn(36) and Asn(147) residues, and phosphate groups bound to some serine residues in the sequence of Ser(185) to Ser(197) as a cluster. These results led us to the conclusion that yolk- and white-RBPs are bio-synthesized from the same gene in the different organs (liver and oviduct). The carbohydrate composition of yolk-RBP was identical to that of plasma-RBP but different from that of white-RBP showing that the processing of the carbohydrate chains in the liver was different from that in the oviduct.