Studies in Amino Acid Utilization

Abstract

The qualitative amino acid requirements for maintenance of the normal adult male rat have been measured using the criteria of preservation of appetite and weight as well as nitrogen balance. A purified amino acid mixture patterned after the composition of casein served as the source of dietary nitrogen in the basal ration. The effects upon appetite and weight following removal of each of the 9 essential amino acids and all of the non-essential amino acids have been observed, as well as the effects of substituting norleucine for leucine or lysine and tyrosine for phenylalanine. When single amino acid deficiencies were studied, pairs of comparable rats, one receiving the complete ration and one the incomplete, were used. In some instances these rations were interchanged at the end of the first 20 days and the experiment was continued for an additional 10 days. Nitrogen balance determinations were made in representative animals during the first 14 days of the experiment, two 7-day collection periods serving as mutual checks. In 1 experiment the force-feeding technique was used to equalize the nitrogen and caloric intakes between the deficient and control rats. The results may be summarized as follows: