p1. Formiminoglutamic acid, a product of the catabolism of histidine, is excreted in abnormally large amounts in the urines of vitamin Bsub12/sub-deficient rats and of vitamin Bsub12/sub-deficient sheep; the excretion is reduced to negligible amounts after administration of vitamin Bsub12/sub. 2. After administration of certain methyl donors to vitamin Bsub12/sub-deficient rats or sheep urinary excretion of formiminoglutamic acid is temporarily decreased. 3. Irrespective of the pteroylglutamic acid status of the animals neither vitamin Bsub12/sub-deficient rats nor vitamin Bsub12/sub-deficient sheep have the ability to deal efficiently with histidine. 4. In sheep, urinary excretion of formiminoglutamic acid is increased after administration of aminopterin; treatment with pteroylglutamic acid restores the ability of the animal to deal with the catabolic products of histidine. 5. The possible functions of vitamin Bsub12/sub and methionine in relieving a virtual deficiency of pteroylglutamic acid are discussed./p
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