THE EFFECT OF SYNTHESIS TEMPERATURE ON THE STRUCTURE OF DEXTRAN NRRL-B-512F

The present study puts together the results from several types of experiments from which the effect of synthesis temperature on the primary structure and the macromolecular characteristics of native dextran NRRL B 512F has been deduced. From light-scattering measurements, it has been concluded that the average molecular weight of non-associated molecules is almost independent of synthesis temperature and much smaller than all the values reported in the literature for non-fractionated native dextran. This result was made possible due to the use of a method which does not take into account the contribution of dextran aggregates. By combining intrinsic viscosity measurements and hydrolysis of dextran with a glucoamylase, evidence is given that branching increases with synthesis temperature, particularly through secondary ramifications. As a result, the conformation of dextran changes from an expanded random coil type at relatively low temperature (<20$DEGC), to a compact solid sphere type observed at higher temperature (30$DEGC).