The nutritive value and safety of D-phenylalanine and D-tyrosine in mice.
Growth studies in mice fed synthetic amino acid diets showed that: 1) the biological utilization of D-phenylalanine relative to its L-isomer ranged from 28-81%, depending on the respective concentrations of these amino acids in the diet; 2) L-tyrosine can replace about one-half of the L-phenylalanine needed to achieve maximum weight gain and 3) D-tyrosine has no similar sparing effect on L-phenylalanine. In fact, addition of D-tyrosine to amino acid or casein diets depressed weight gain to 10% that of the control. This inhibition was significantly reduced by increasing the L-phenylalanine content of the amino acid diets and the protein content of the casein diets. Growth inhibition, therefore, appears to be related to the ratio of D-tyrosine to L-phenylalanine and possibly other amino acids in the diet, rather than to the absolute levels of D-tyrosine. Mechanistic rationalizations are offered to account for the toxic or antinutritional manifestation of D-tyrosine.
D000821:Animal Feed; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D005527:Food, Fortified; D051379:Mice; D008815:Mice, Inbred Strains; D009753:Nutritive Value; D010649:Phenylalanine / Q000378:metabolism* / Q000633:toxicity; D013237:Stereoisomerism; D014443:Tyrosine / Q000378:metabolism* / Q000633:toxicity
D014443:Tyrosine; D010649:Phenylalanine