Biochemical and Molecular Action of Nutrients Research Communication Kinetics of Carnitine Palmitoyltransferase-I Are Altered by Dietary Variables and Suggest a Metabolic Need for Supplemental Carnitine in Young Pigs

To examine the kinetics of carnitine palmitoyltransferase-I (CPT-I) and the influence of dietary variables, young pigs (18 kg, n 5 20) were fed corn-soybean meal diets supplemented with 40 g soy oil/kg and containing either 136 or 180 g crude protein/kg and either 0 or 500 mg/kg L-carnitine (2 3 2 factorial design). Diets were offered for 10 d (85% of ad libitum); CPT-I activities in liver and skeletal muscle mitochondria were determined, and enzyme kinetic constants (Vmax and Km for carnitine) were estimated. Kinetics of CPT-I in muscle were not affected by diet (P > 0.1; carnitine Km 5 480 6 44 mmol/L). In contrast, the Km for carnitine in liver was increased from 164 to 216 6 20 mmol/L by dietary L-carnitine supplementation (P < 0.01) and from 169 to 211 6 20 mmol/L by high protein feeding (P < 0.05). Dietary Lcarnitine increased muscle and liver free carnitine concentrations by 72 and 158% over control concentrations (770 and 80 mmol/kg wet muscle and liver, respectively). Because tissue carnitine concentrations were within the range of the respective Km for both liver and muscle tissue, it is inferred that alteration of tissue carnitine concentrations via dietary supplementation could modulate CPT-I activity in young pigs. J. Nutr. 130: 2467–2470, 2000.