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Comparative Utilization of the -Keto and D- and L--Hydroxy Analogs of Leucine, Isoleucine and Valine by Chicks and Rats^1,2,

Department of Animal Science, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Several experiments were conducted to quantitatively evaluate the growth-promoting capacity of the isomers of the branched-chain amino acids (BCAA) and their -hydroxy and -keto analogs for the chick and rat. Basal chemically defined diets were formulated to be singly deficient in the BCAA under study; analogs therefore were evaluated as sources of supplemental amino acid activity. DL-Isoleucine (DL-Ile), -keto-ß-L-methylvaleric acid (KMV) and the isomers of -hydroxy-ß-methylvaleric acid (HMV) were inferior to an isomolar level of L-Ile and varied considerably in their capacity to support growth of chicks and rats. Efficacy values of the compounds for chicks (C) and rats (R) were: DL-Ile 85% (C), 58% (R); KMV 60% (C), 38% (R); L-HMV 84% (C), 65% (R); DL-HMV 49% (C), 45% (R); and D-HMV -10% (C), -2% (R). The isomers of valine (Val) and -hydroxyisovaleric acid (HIV) had efficacy values in chicks of: DL-Val, 84%; D-Val, 72%; L-HIV, 82%; DL-HIV, 79%; D-HIV, 66%. D-Val had only marginal growth-promoting activity for rats, 16%. All Val analogs had comparable efficacy values for the rat: -ketoisovaleric acid (KIV), 49%; L-HIV, 54%; DL-HIV, 51%; and D-HIV, 46%. DL-Leu and D-Leu, -ketoisocaproic acid (KIC), and L-, DL- and D--hydroxyisocaproic acid (HIC) were all less efficacious than isomolar amounts of supplemental L-Leu in rats. Efficacy values were: DL-Leu, 78%; D-Leu, 48%; KIC, 56%; L-HIC, 58%; DL-HIC, 55%; and D-HIC, 41%. The BCAA keto analogs were not superior to the L--hydroxy analogs in growth-promoting capacity, and this is of great interest for the potential use of these nitrogen-free amino acid analogs in nutritional therapy.

KEY WORDS: • branched-chain amino acids • leucine • isoleucine • valine • branched-chain keto analogs • branched-chain hydroxy analogs • isomeric utilization • analog efficacy

¹ A preliminary report of chick experiments has been published. Boebel, K. P. & Baker, D. H. (1981) Comparative utilization of the isomers of valine and isoleucine and their respective hydroxy-analogs by the chick. Poult. Sci. 60, 1626–1627.

² Part of a thesis by K.P.B. submitted to the Graduate College of the University of Illinois in partial fulfillment of the requirements for the Ph.D. degree in Animal Science.

³ To whom reprint requests should be addressed.

Manuscript received 12 April 1982.