CARBOHYDRATE-METABOLISM IN DICTYOSTELIUM-DISCOIDEUM .2. SYSTEMS-ANALYSIS

A transition model of carbohydrate metabolism during differentiation of Dictyostelium discoideum was described in Wright and Albe (1994, J. theor. Biol. 168, 231-241). From this base model, two steady-state models are derived in which concentration and flux are consistent with culmination (600 min) or young sorocarp (700 min) stages of development. These steady-state models are analyzed using metabolic control theory (MCT), and the summation property is met for metabolites, individual flux rates, and overall flux control coefficients. The MCT analyses show that flux control differs between the two stages. At culmination, cellulose synthetase is the major control point for overall pathway flux (C = 0.86) whereas at young sorocarp, glycogen phosphorylase is the major control point (C = 0.89). This is a reflection of the increased competition between the endproduct synthases, which are used to define overall pathway flux. Thus the specific metabolic state of the cells is important in assessing control distribution. The significance of this work in understanding the mechanisms controlling biochemical differentiation is discussed and related to the work of others in the field. For example, mutant analysis can reveal which enzymes are essential to differentiation (most are) but cannot reveal which enzymes are essential to differentiation (most are) but cannot reveal which enzymes are unique and/or rate-controlling.