DIETARY-PROTEIN AND AMINO-ACID LEVELS ALTER THREONINE DEHYDROGENASE-ACTIVITY IN HEPATIC MITOCHONDRIA OF GALLUS-DOMESTICUS

Experiments were conducted to determine if hepatic threonine dehydroge nase (TDH) activity is influenced by dietary protein or specific amino acid concentrations. In an initial experiment, young chicks were depr ived of feed for 60 h or had access for 72 h to a 22% protein basal di et, a protein-free diet or a 51% high protein diet. TDH activity was d etermined as aminoacetone and glycine accumulation during incubation o f liver mitochondria. TDH activity was significantly (P < 0.01) lower in chicks fed the protein-free diet and significantly greater in chick s fed the high protein diet compared with chicks fed the basal diet. F ood deprivation had no effect on TDH activity. A second experiment was conducted using the 22 and 51% protein diets, the 22% protein diet pl us 1.14 g/100 g diet threonine (equivalent to the free plus protein-bo und threonine content of the high protein diet), and the 51% protein d iet containing 0.15 g/100 g diet less threonine. TDH was increased in chicks fed either high protein diet (P < 0.05). There were no signific ant differences in TDH activity, however, between chicks fed the basal diet and the threonine-supplemented diet or between chicks fed the tw o high protein diets. In two other experiments, the activity of TDH wa s investigated in chicks fed for 9 d dietary supplements of either ser ine or glycine (5.5 or 4 g/100 g basal diet, respectively). The supple ments were added to the basal diet or the basal diet imbalanced by the addition of 6% branched-chain amino acids. Neither the serine nor the glycine supplement significantly altered TDH activity or the increase d activity associated with a branched-chain amino acid-induced threoni ne imbalance. The results suggest that hepatic TDH activity is influen ced by protein level or other amino acids more than by threonine itsel f.