Structural stability of (1->3)-beta-D-glucan macrocycles

The long-term stability of the distribution of macromolecular topologies of the alkaline treated (1->3)-beta-D-glucan, scleroglucan (1.0 mg/ml), was investigated using HPLC and electron microscopy. The fraction of cyclic (C) and linear (L) topologies of the samples renatured from alkaline solution when [NaOH] was 0.35 M or higher, remained in most cases constant following storage in neutral aqueous solution for 18 months at room temperature. Electron microscopy revealed a reduction of C and increase of L following the long-term storage for scleroglucan renatured from [NaOH] less than 0.25 M. Annealing of renatured samples at temperature Ta equal 100°C gave rise to a stable distribution of 60% cyclic and 13% linear topologies. Increasing Ta above 100°C yielded a distribution of topologies that reduced in initial cyclic fraction from 17% to 5 ±3% for Ta=133°C following the 18 months storage. These changes in the distribution of topologies manifested itself also in changes in the HPLC elution profiles. In particular, the solvent history producing long-term structurally stable distribution of species of the annealed sample (Ta=100°C) also yielded unchanged HPLC elution profiles. Our data suggest that rearrangements of quenched imperfections in a reassembled partly triple-helical structure may explain the observed changes in the relative amounts of the linear and circular macromolecular topologies occurring during the storage.