THE METHIONINE AND CYSTINE CONTENT OF HEN'S EGGS

At the 1941 annual meeting of t,he American Society of Biological Chemists, one of us presented evidence that the amino acid composition of the egg may be influenced by feeding the hen a diet rich in protein (1). We now offer experimental results showing how the methionine and cystine content of the egg can be changed by varying the protein in the hen’s diet according to its high or low methionine content. McFarlane, Fulmer, and Jukes (2) found no changes in the amino acid composition of the egg proteins when they varied the basal diet of the hens from 10 to 16 per cent crude protein. A higher protein supplement, as a dietary influence would have been more appropriate to test the constancy of the amino acid composition of the egg proteins. r’alvery and Titus (3) did not observe any change in the amino nitrogen distribution in egg albumin and vitellin prepared from eggs laid by hens fed a diet in which the protein n-as furnished exclusively by wheat, corn, or soy bean. Similar feeding experiments were carried out with pigeons by Gerber and Carr (4). They observed differences in the N distribution in the egg proteins (Van Slyke) and in the immunological behavior in rats sensitized to egg prot.eins. Their finding points to the probability of change in the amino acid composition of the egg protein induced by the ingestion of the various feeds. If the amino acid composition of the different egg proteins is considered constant, then an increase in an amino acid in the egg may mean that the protein content of the egg has increased or that the proportions of the various egg proteins have changed. An increase in total protein content would naturally bring about proportional increases in all of the amino acids, and the cystine-methionine ratio would not be changed. However, we will show that the cystine-methionine ratio does not remain constant and that the levels of these two amino acids are independent of the t.ot.al N in the wg. Variations in the protein components of egg white were noted by Longsworth, Cannan, and MacInnes (5). They found that the albumin content