Mitochondrial lysine uptake limits hepatic lysine oxidation in rats fed diets containing 5, 20 or 60% casein.
Sixty male Sprague-Dawley rats were randomly allotted to receive diets containing 5, 20 or 60% casein. Rats had access to the diet only during the initial 8 h of the daily 12-h dark period. Hepatic mitochondrial lysine uptake, lysine alpha-ketoglutarate reductase (LKR) and saccharopine dehydrogenase (SacD) activities, and in vitro lysine oxidation (LOX) were measured 0, 6, 12, 18 and 24 h after the start of the dark period. Diurnal variation of mitochondrial lysine uptake was not detected (P > 0.10) although uptake varied 3-fold over 24 h. Mitochondrial lysine uptake was greater (P < 0.05) for rats fed diets containing 60% casein than for rats fed diets containing 5% casein. Diurnal variation of LKR was detected (P < 0. 05) in rats fed diets containing 20 and 60% casein. Diurnal variation of SacD was detected (P < 0.05) in rats fed diets containing 60% casein. Increased casein consumption resulted in increased LKR and SacD activities (4- to 5-fold; P < 0.05). Diurnal variation of LOX was detected in rats fed diets containing 20 and 60% casein (P < 0.05). Increasing the casein concentration in the diet from 5 to 60% resulted in a 7-fold increase in LOX (P < 0.05). To make rate comparisons, LKR and SacD activities and LOX were predicted from a range of substrate concentrations (0.1 to 5.0 mmol/L). Overall, LKR and SacD were 6-107 times that of LOX, suggesting that, in liver, mitochondrial lysine uptake limits LOX.
Blemings
K P
KP
Department of Department of Animal Sciences, University of Wisconsin Madison, Madison, Wisconsin 53706, USA.
Crenshaw
T D
TD
Benevenga
N J
NJ
D000284:Administration, Oral; D000704:Analysis of Variance; D000818:Animals; D002364:Caseins / Q000008:administration & dosage / Q000494:pharmacology*; D002940:Circadian Rhythm; D004032:Diet; D004305:Dose-Response Relationship, Drug; D008239:Lysine / Q000378:metabolism*; D008297:Male; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D010084:Oxidation-Reduction; D051381:Rats; D017207:Rats, Sprague-Dawley; D012443:Saccharopine Dehydrogenases / Q000378:metabolism; D015430:Weight Gain / Q000187:drug effects
D002364:Caseins; D012443:Saccharopine Dehydrogenases; D008239:Lysine