ISOTOPIC INTERACTIONS BETWEEN CARBOHYDRATE AND PROTEIN-TURNOVER

A reasonably plausible model representing the interactions between car bohydrate, protein and lipid metabolism in the fasted state is present ed. Using computer solutions, we fit the model to literature data. The data and model are insufficient for totally rigorous conclusions, but they suggest tentatively that in 60 hr fasted man, a considerable fra ction of the gluconeogenic flux may proceed (in the liver or kidney) d irectly from Krebs cycle intermediates, not through pyruvate. Using th e [U-C-14]glucose incorporation into protein found by Shipley et al. [ Am. J. Physiol. 213: 1149-1158, 1967], we illustrate the effect that t he isotopic interactions betwen protein and carbohydrate turnover have in making difficult the use of simple models, e.g. for the estimation of gluconeogenesis. Ne also outline a possible approach for the estim ation of the kidney contribution to gluconeogenesis.