Utilization of the L- and DL-isomers of alpha-keto-beta-methylvaleric acid by rats and comparative efficacy of the keto analogs of branched-chain amino acids provided as ornithine, lysine and histidine salts

Abstract

Three experiments were conducted to quantitatively evaluate the growth-promoting capacity of alpha-keto analogs of the branched-chain amino acids (BCAA). 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. Analogs of isoleucine tested included alpha-keto-beta-L-methylvalerate (L-KMV) as the Na salt (L-KMV-Na) and alpha-keto-beta-DL-methylvalerate (DL-KMV) as the Na (DL-KMV-Na), ornithine (DL-KMV-Orn) and lysine (DL-KMV-Lys) salts. Slope-ratio efficacy values were L-KMV-Na, 65%; DL-KMV-Na, 44%; DL-KMV-Orn, 41%; DL-KMV-Lys, 43%. Alloisoleucine accumulated in the plasma of rats fed all sources of KMV, but its concentration was three times greater when DL-KMV was fed than when L-KMV was fed. The analog of valine tested was alpha-ketoisovalerate as the ornithine (KIV-Orn) or lysine (KIV-Lys) salts. There was no significant difference in efficacy between salts (47 versus 44%, respectively). The analog of leucine, alpha-ketoisocaproate, was given as the ornithine (KIC-Orn), lysine (KIC-Lys) and histidine (KIC-His) salts with resulting efficacies of 50, 38 and 49%, respectively. Slope-ratio efficacies of KIC-Orn and KIC-His were statistically similar and efficacy of KIC-Lys was inferior to both KIC-Orn and KIC-His.