Transfer of carbon from formate to amino acids of milk protein in the intact cow

¹ University of California School of Veterinary Medicine and College of Agriculture, Davis, California

C¹⁴-formate was injected intravenously into two lactating cows or infused into the cistern of a quarter of the udder in a third cow. Several amino acids were recovered from milk protein collected at intervals during a 36-hr period after the C¹⁴-formate was injected. The amino acids were assayed for C¹⁴ and, in the case of serine and methionine, degraded to establish the intramolecular C¹⁴ distribution. The C¹⁴ was found to be confined largely to the hydroxymethyl carbon of serine and to the methyl carbon of methionine. Relatively little C¹⁴ was present in other positions of these amino acids or in the other amino acids normally synthesized by the lactating cow, showing that formate carbon was confined to a very limited pool during utilization. The incorporation of formate carbon into amino acids apparently takes place largely outside the udder, presumably in the liver.