The Concentration and Assay of Avidin, the Injury-producing Protein in Raw Egg White

When the tissues of chicks maintained on a diet containing unheated egg white were found to be deficient in biotin in spite of the abundance of this vitamin in the diet (l), it was concluded that the injury caused by the egg white is not due to any direct toxin but rather is produced indirectly by the action of the egg white in making the biotin of the diet unavailable to the animal. To support this conclusion, experiments were performed to determine the possibility of inactivating biotin in vitro with egg white. The successful demonstration of this inactivation was reported in a recent note to this Journal (2), in which it was stated (a) that biotin readily combines with a protein constituent of unheated egg white to form a stable complex from which the biotin cannot be recovered by dialysis, (b) that yeast is unable to utilize biotin when the protein is present in the culture medium, and (c) that the combination between the active protein and biotin is stoichiometric and is not materially affected by impurities in the concentrates. An adaptation of the biotin test method developed in this laboratory (3) made it possible to follow the biotin-inactivating component in the fractionation of egg white proteins and to develop the concentration method which was outlined. It appeared probable that the substance being concentrated which rendered the biotin unavailable to yeast was identical with the constituent in raw egg white responsible for the injury to animals. This identity has been recently confirmed (4), as highly active concen-