The antibacterial activity of the egg white protein conalbumin.

Conalbumin is an egg white protein that inhibits growth of microorganisms by forming a pink-colored, remarkably stable complex with iron. Although the antibacterial activity of egg white has long been known, the existence of such an iron binding agent was not recognized priQr to the report of Schade and Caroline in 1944. In 1946 conalbumin was identified as the agent responsible for the antibacterial activity due to iron binding and for the pink discoloration of egg white containing iron (Schaible and Bandemer, 1946; Alderton, Ward, and Fevold, 1946). Warner and Weber (1951) have recently reported the preparation of conalbumin in crystalline form. Interest in conalbumin has been stimulated by its close similarity to siderophilin, the pl3-metal-binding globulin from mammalian plasma (Fiala and Burk, 1949; Schade, Reinhart, and Levy, 1949). Recent studies at this laboratory concerned the chemical groupings in conalbumin responsible for its iron binding properties and the mechanisms by which a test organism, Micrococcus pyogenes var. albus, is capable of delayed growth in the presence of inhibitory amounts of conalbumin (Fraenkel-Conrat and Feeney, 1950). It was postulated that the organism may overcome inhibition by utilizing the free iron in equilibrium with the iron-conalbumin complex and not by destroying the protein or by its own adaptation to an iron deficiency. These studies have since been extended and one phase has been recently reported (Feeney, 1951). In this recently reported phase it was found that inhibition by conalbuimin could be largely prevented by the addition of 8-hydroxyquinoline and that this prevention was intimately related to the iron and cobalt contents of the medium. The present report presents results of the main phase of the extended studies and describes efforts to further characterize the mechanism of action of this protein on several organisms. The investigations include studies on the influence of variations in cultural conditions and comparisons with several nonprotein metal-ion complexing agents and the iron-complexing, synthetic, protein derivative, hydroxylamido ovomucoid (Fraenkel-Conrat, 1950).