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The Quantitative Amino Acid Requirements of Young Women

IV. Phenylalanine, with and Without Tyrosine¹

Two Figures

Nebraska Agricultural Experiment Station, University of Nebraska, Lincoln

Ten college girls served as subjects in a study of the requirement for phenylalanine with and without tyrosine. On a semi-purified diet the daily phenylalanine intake was reduced from 1280 to 320, to 220, to 120, and to 70 mg, while the tyrosine intake was kept constant at 900 mg daily. An intake of 220 mg of phenylalanine was the least amount which maintained all of the subjects in nitrogen equilibrium, defined as the condition in which nitrogen excretion remains within 95 to 105% of the intake. The effect of feeding other proportions of phenylalanine and tyrosine was studied but no clear-cut relationships were established. However, the sparing action of tyrosine on phenylalanine requirement was evident.

Another group of 8 subjects remained in the zone of nitrogen equilibrium when fed a Test Mix ration which included 220 mg of phenylalanine, 900 mg of tyrosine, and minimum amounts of threonine, valine, tryptophan and leucine found in this laboratory to be required by young women for maintaining nitrogen balance.

In the presence of 900 mg of tyrosine, 220 mg of phenylalanine is suggested as the tentative minimum daily requirement of young women.

² Present address: Division of Home Economics, Oklahoma A. & M. College, Stillwater.

³ Present address: Spokane, Washington.

Manuscript received 21 September 1955.

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