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This study attempted to determine whether the quantity and the quality of protein intake could influence the activity of some enzymes involved in carbohydrate metabolism. Thus, adult rats were fed for 23 days a diet containing different levels (10 to 70%) and qualities (casein, wheat gluten, and egg yolk) of protein. Variations in liver enzyme activities of pyruvate kinase (PK), glucose-6-phosphate dehydrogenase (G6PDH), malic enzyme (ME), glucose-6-phosphatase (G6Pase), and phosphoenolpyruvate carboxykinase (PEPCK) were studied. Also the changes in enzyme activities were compared with changes in food intake and body weight gain. Increasing the protein level produced a progressive fall in the activities of ME and PK. The decrease in PK activity was greater when the biological value of the dietary proteins was higher (P less than 0.05). On the other hand, the activities of G6PDH and PEPCK increased as the protein level increased. The activity of G6Pase was unchanged. The relationship between the two opposing enzyme activities PK and PEPCK, in relation to protein intake, shows that for each protein studied, the equilibrium between glycolysis and gluconeogenesis was obtained at different protein intakes (1.5, 1.9, and 2.2 g of protein/day/100 g of body weight, respectively, for egg yolk, casein, and wheat gluten) regardless of daily consumption of energy as carbohydrate, which are similar (8 to 9 kcal/day/100 g of body weight). This equilibrium also corresponded to the maximum weight gain (5 g) of the experimental animals. In conclusion, the experimental method used permits a simultaneous assessment of the protein and carbohydrate requirements ensuring the best weight gain in young adult rats.

SOMMAIREPrivée de riboflavine, la poule pondeuse transfère cette vitamine dans l'oeuf aux dépens deses propres tissus. Elle peut ainsi sacrifier plus de la moitié de son capital hépatique en riboflavine pour assurer la ponte. Le

Activities of enzymes involved in glucose phosphorylation, glucokinase (EC 2.7.1.2.), hexokinase (EC 2.7.1.1.), glucose 6-phosphatase (EC 3.1.3.9.), and in NADPH production, glucose-6-phosphate dehydrogenase (EC 1.1.1.49), 6-phospho-gluconate dehydrogenase (EC 1.1.1.44), NADP Malate-dehydrogenase (EC 1.1.1.40), were studied in rat liver and adipose tissue during fasting-refeeding and protein depletion-repletion. Fasting induced an increased activity of glucose-6-phosphatase and a sharp decrease in all other activities in both liver and adipose tissue hexokinase, dehydrogenases of the pentose shunt and NADP-Malate dehydrogenase. These activities have long been associated with adaptative hyperlipogenesis. In our experiments adaptation was more evident in liver than adipose tissue. On the other hand, protein-depletion alone did not change glucose availability or glucose 6-phosphatase activity. Protein repletion did not induce any hyperactivity of glucokinase, adipose tissue hexokinase, nor dehydrogenases, evidencing a lack of hyper-lipogenesis.

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