Comparison of Avian Egg White Conalbumins.

Conalbumin is a specific metal-binding protein found in egg white (I, 2). It forms a stable red complex with 2 atoms of iron per molecule (3-5) and a less stable yellow complex with 2 atoms of copper (3, 5). A still weaker nonchromogenic complex is formed with zinc (5). The molecule contains no special prosthetic groups for binding metal ions. Thus, the metal-binding property appears to be intimately related to the fundamental properties and conformation of the protein molecule (3). In most respects conalbumin is very similar to the metal-binding protein, serum transferrin (6, 7), and studies on these two proteins (7) are mutually beneficial to the understanding of the metal-binding properties of both. The physical heterogeneity of chicken conalbumin has received particular attention. Longsworth, Cannan, and MacInnes (8) reported that conalbumin undergoes reversible changes in acid solutions (below pH 4) which result in the formation of electrophoretically separable multiple forms. Further investigation by Cann and Phelps (Q-11) indicated that at low pH electrolyte binding and aggregation resulted in the formation of physically distinguishable conalbumin species. Physical studies at neutral and slightly alkaline pH values have shown the protein to be homogeneous (4, 12-14) with no indication of aggregation (13, 14). Fuller and Briggs (13) have shown that formation of the iron-conalbumin complex does not result in aggregation. Recently, Lush (15) reported two conalbumin components when chicken egg white was subjected to starch gel electrophoresis. This observation has been confirmed by Feeney et al. (16) and others (17, 18). Ogden et al. (18) have reported the conalbumins of the egg whites of one chicken strain to vary genetically. The b type consisted of the two components observed by Lush and others (15-17). Upon starch gel electrophoresis the a type showed two conalbumin components, the slower of which moved coincident with the fast component of type 6. The ab type existed in the strain, and the electrophoretic pattern consisted of three conalbumin bands with mobilities corresponding to those in the a and 6 types. In the recent genetic study of a chicken egg white protein, Feeney et al. (16) observed no genetic variation in the conalbumins. The present investigation compares the general properties of chicken egg white conalbumin with those of the conalbumins