Threonine metabolism in vivo: effect of threonine intake and prior induction of threonine dehydratase in rats.
The metabolic fate of threonine was investigated in young male rats fed 15% amino acid diets containing from 0.15% to 0.85% of L-threonine. Liver serine-threonine dehydratase (S-TDH) activity did not increase with increasing dietary threonine content. The level of threonine required for maximum weight gain was not greater than 0.55% of the diet (or about 600 mumoles/day). Tissue free threonine content of rats fed the diets with 0.15% or 0.3% of threonine was very low but increased sharply with increasing dietary threonine content above 0.3%. During ad libitum feeding of these diets containing L-[U-14C]threonine, rate of oxidation of threonine was low when intake was in the range of the requirement for maximum growth, but increased, thereafter as threonine intake increased. A 30-fold induction of liver S-TDH, by prior feeding of an 80% casein diet, did not result in increased oxidation of threonine when dietary threonine content was 0.15%. When dietary threonine content was increased to 0.5%, oxidation of threonine increased slightly but significantly. With 3% of threonine in the diet, rats previously fed a 15% casein diet had extremely high tissue threonine concentrations whereas those with high S-TDH activity, due to the previous feeding of the 80% casein diet, oxidized threonine rapidly and tissue threonine concentrations were elevated much less.
D000818:Animals; D001835:Body Weight; D002364:Caseins / Q000008:administration & dosage; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction / Q000187:drug effects; D008099:Liver / Q000201:enzymology*; D008297:Male; D010084:Oxidation-Reduction; D051381:Rats; D013912:Threonine / Q000378:metabolism* / Q000494:pharmacology; D013913:Threonine Dehydratase / Q000096:biosynthesis*; D014018:Tissue Distribution
D002364:Caseins; D013912:Threonine; D013913:Threonine Dehydratase