title: Threonine is catabolized by L-threonine 3-dehydrogenase and threonine dehydratase in hepatocytes from domestic cats (Felis domestica).
abstract: Isolated hepatocytes were used to study threonine catabolism in kittens, and dietary threonine and crude protein were varied to study enzyme adaptation. Cells were isolated from 21-wk-old kittens which had been fed diets containing threonine at 4 or 8 g/kg of diet with either 200 or 500 g crude protein/kg of diet (2 x 2 factorial, n = 4/group). Production of CO2, glucose and various metabolites from [U-14C]threonine were measured. Inclusion of 10 mmol/L glycine, or glycine in combination with 10 mmol/L acetaldehyde +ethanol, in the incubation medium decreased formation of 14CO2 and [14C]glucose. At the same time, large amounts of [14C]glycine but no [14C]ethanol was formed. Inclusion of 10 mmol/L 2-ketobutyrate + 2-hydroxybutyrate decreased 14CO2 but not [14C]glucose production and resulted in the formation of [14C]2-hydroxybutyrate. Under all incubation conditions, 14CO2 and [14C]glucose production changed in response to alterations in dietary protein but not dietary threonine. It appears that threonine dehydratase and L-threonine 3-dehydrogenase, but not threonine aldolase, are active pathways for threonine metabolism in cats, and both enzymes are sensitive to levels of dietary protein.
authors.affiliation: Department of Molecular Biosciences, University of California, Davis 95616, USA.
authors.forename: V A
authors.initials: VA
authors.lastname: Hammer
authors.forename: Q R
authors.initials: QR
authors.lastname: Rogers
authors.forename: R A
authors.initials: RA
authors.lastname: Freedland
mesh_terms: D000079:Acetaldehyde / Q000378:metabolism; D000429:Alcohol Oxidoreductases / Q000378:metabolism* / Q000502:physiology; D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism; D002415:Cats / Q000378:metabolism*; D002478:Cells, Cultured; D000431:Ethanol / Q000378:metabolism; D005260:Female; D005947:Glucose / Q000378:metabolism; D005998:Glycine / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D011765:Pyruvaldehyde / Q000378:metabolism; D013047:Specific Pathogen-Free Organisms; D013912:Threonine / Q000378:metabolism*; D013913:Threonine Dehydratase / Q000378:metabolism* / Q000502:physiology
chemical_list: D002245:Carbon Dioxide; D013912:Threonine; D000431:Ethanol; D011765:Pyruvaldehyde; D000429:Alcohol Oxidoreductases; C023159:L-threonine 3-dehydrogenase; D013913:Threonine Dehydratase; D000079:Acetaldehyde; D005947:Glucose; D005998:Glycine