STUDIES OF THE EFFECT OF DIETARY PROTEIN AND CALORIC LEVELS ON THE KINETICS OF NITROGEN METABOLISM USING N15 L-ASPARTIC ACID

Abstract

The mathematical model of N metabolism proposed by San Pietro and Rittenberg (Jour. Biol. Chem. 201, 457, 1953) has been examined from the theoretical and experimental standpoint. Ah extension of the mathematical reasoning has led to a method for computing the rate constant for metabolic pool turnover (B), metabolic pool size (P), and rate of incorporation of N into protein (S) at any time during the experiment. Four pairs of duplicate studies on 4 different diets were carried out on a patient on a metabolic balance study. The reproducibility of calculated valves (B, P and S) in one individual under the same conditions was adequate enough to suggest that the effect of variables on the kinetics of N metabolism can be readily determined. The rate constant for nitrogenous metabolic pool turnover does not appear to vary significantly with the changes of diet studied. Increased protein intake apparently increases the size of the metabolic pool (P) somewhat. The calculated rate of incorporation of N into protein (S) increased when both the caloric and protein intake were increased, even though the patient remained in N equilibrium.