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Efficiency of Phenylpyruvic and Phenyllactic Acids as Substitutes for Phenylalanine in the Diet of the Growing Rat1

Alan R. Gaby and Rajender K. Chawla

Departments of Biochemistry, Medicine and Surgery, Emory University School of Medicine, Atlanta, Georgia 30322

Male weanling albino rats fed a diet containing all nutrients for optimal growth, including 45.4 µmoles of phenylalanine/g, gained weight at an average of 6.5 g/day. Removal of phenylalanine caused an average weight loss of 1.1 g/day. Addition of graduated increments of phenylalanine led to progressive increases in growth rate; the increases being proportional to the dietary content of this amino acid. When phenylpyruvic or L-phenyllactic acids were added isonitrogenously to the phenylalanine-free diet, growth rate also increased. Percent efficiency of these amino acid analogues as dietary substitutes for phenylalanine, calculated as
Figure 1
varied from 50% to 70% for phenylpyruvic acid and 65% to 95% for L-phenyllactic acid. Efficiency increased as dose of analogue increased. Non-isonitrogenous substition did not change growth rates. Supplementation with a megadose of pyridoxine did not increase the efficiency of phenylpyruvic acid. D-phenyllactic acid and cinnamic acid were completely ineffective as substitutes for phenylalanine. When tyrosine was withdrawn from the diet, efficiency of phenylpyruvic acid was 70% at several doses. The efficiency of L-phenyllactic acid was 65 to 40%, decreasing with increasing dose.

KEY WORDS: • phenylalanine • phenylpyruvic acid • phenyllactic acid • alpha-keto acids • alpha-hydroxy acids

1 This investigation was supported by U.S. Public Health Service Grants AM 15736 and RR 00039.

Manuscript received 28 July 1975.




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