PROTEIN EVALUATION AND PROTEIN METABOLISM

Abstract

Experiment with pigs revealed in the blood serum a high negative correlation between the biological value (BV) of the dietary protein and the activities of arginase, glutamic-oxalacetic transaminase and leucine aminopeptidase. We found also in the rat liver analogous negative correlation between BV and the activities of arginase, ornithine carbamyl transferase and glutamic-pyruvic transaminase. The determination of the blood urea concentration in rats, pigs or men, is under suitable experimental conditions an elegant measuring technique for protein quality. Our new method of labelling the animals with 15N may be suitable for an exact protein evaluation in maintenance, Rats received a casein diet with 15N labelled CH3COONH4 for seven days. After this period the rats received 8 different protein diets adapted to maintenance for 5 days. The excretion of 15N in urine was higher after feeding proteins with low BV. The order of protein quality for maintenance acording to this method was as follows: Fish meal, casein, wheat, whole egg, soybean, yeast, pea and gelatin. For Determination of amino acid requirements in maintenance rats received diets suplemented with graded amounts of L-lysin. After a feeding period of 7 days the animals received 3H and 14C-lysin or 15N-lysin injected intraperitonally. The level of excretion of 14C-activity through CO2 and that of specific 14C-activity of CO2 or 15N in urine increased with increasing lysine concentrations. This produced a broken curve pattern, which is suitable for estimation of amino acid requirement in maintenance or growth.