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Amino Acids in the Urine of Human Subjects Fed Eggs or Soy Beans¹

Departments of Biochemistry and Home Economics, College of Agriculture, University of Wisconsin, Madison

1. Diets containing eggs or soy beans as sources of protein were fed to 4 human subjects at a protein level corresponding to 5% of the ingested calories, and the amino acid content of the urine was determined microbiologically.

2. Cystine was invariably found to be excreted in the highest percentage of the amount ingested, 12 to 44%. Histidine was next, 4 to 8%. The percentage excretion for most amino acids was found to range from about 0.2 to 1.8% of that ingested. Proline, lysine, and isoleucine were frequently absent from the specimens of urine analyzed, free aspartic acid was always absent, while leucine was present only when the subjects were in negative balance (autoclaved soy bean diet).

3. There were no group differences between the excretion of essential and non-essential amino acids.

4. The hydrolysis of urine resulted in appreciable increases in microbiologically available tyrosine, serine, tryptophane, and aspartic acid. Apparently many amino acids in human urine were bound as peptides.

Manuscript received 23 September 1946.