The Effect of Choline on the Ability of Homocystine to Replace Methionine in the Diet*

In a previous communication it was reported that under certain dietary conditions, depending on the source of the vitamin B complex, homocystine was incapable of replacing methionine for the support of growth of animals on a cystine-methionine-free diet (l), a finding which was corroborated by Rose and Rice (2). On the other hand we were able to confirm their observation that with tikitiki and milk vitamin concentrate as the source of the B complex, homocystine could support suboptimal growth (I., 2). From these studies it was inferred that some unknown factor was necessary for the methylation of homocystine (homocysteine), and work toward t’he isolation of the factor was undertaken. In the previous investigation, it was noted that the livers of the animals appeared yellowish at autopsy, and histological examination yielded findings indicative of fatty infilt,ration of the liver (1). The diet employed contained 31 per cent fat and since choline was known to inhibit fatty infiltration of the liver of animals on a high fat diet a suspicion arose t,hat the diet employed might possibly be deficient in choline. As a preliminary step to embarking on the isolation of the unknown factor, the previous work was once again repeated. The amino acid diet, patterned after that of Rose, was again employed. It was also supplemented by the vitamin B mixture we had previously used; namely, thiamine chloride, riboflavin, nicotinic acid, and small amounts of ryzamin-B. It was under