Incorporation of 75Se-Selenomethionine and 35S-Methionine into Chicken Egg White Proteins

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Abstract
After the simultaneous injection of trace amounts of 75Se-selenomethionine and 35S-methionine into the wing vein of the hen, the extent and mode of incorporation of both amino acids into the egg white proteins was studied. The results obtained appear to indicate that the selenomethionine is incorporated in a manner indistinguishable from that of methionine. All of the 75Se associated with the proteins was identified as 75Se-selenomethionine. The amino acid appears to be bound to the protein by covalent linkages since it is not removed by dialysis, gel-filtration or precipitation by trichloroacetic acid. The ratio of 35S/75Se of the total egg white proteins is approximately maintained during several manipulations of the proteins including the isolation of crystalline ovalbumin and in the amino acids liberated during the proteolytic digestion of this protein. The only gross difference observed in the behavior of both amino acids is the absence from the protein hydrolysates of any 75Se-selenocysteine although 35S-cysteine was detected.