The effect of copper on the concentrations of o- and m-tyrosines in the serum of guinea pigs was studied in vivo. When guinea pigs were fed the normal diet and 0.1% CuSO4 solution as a drinking water for 13 d, the concentrations of o-and m-tyrosines in the serum increased more significantly than that of guinea pigs fed normal diet and water without copper. Phenylalanine hydroxylase in the liver and kidney, and tyrosine hydroxylase in the brain and adrenal were not activated by the administration of copper to guinea pigs. The administration of copper caused an abnormal accumulation of copper in the liver, but not in the kidney, adrenal and brain, and significantly depressed the ascorbic acid content in various organs including the liver, kidney, brain and adrenal. The results obtained suggest that o-and m-tyrosines may be also formed nonenzymatically in vivo, in addition to the formation by the participation of enzymes such as phenylalanine and tyrosine hydroxylases.
