Structural stability of (1→3)-β-D-glucan macrocycles

The long-term stability of the distribution of macromolecular topologies of the alkaline treated (1 --> 3)-beta -n-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 T-a equal 100 degreesC gave rise to a stable distribution of 60% cyclic and 13% linear topologies. Increasing T-a above 100 degreesC yielded a distribution of topologies that reduced in initial cyclic fraction from 17% to 5 +/- 3% for T-a = 133 degreesC 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 (T-a = 100 degreesC) also yielded unchanged HPLC elution profiles. Our data suggest that rearrangements of quenched imperfections in a re-assembled partly triple-helical structure may explain the observed changes in the relative amounts of the linear and circular macromolecular topologies occurring during the storage. (C) 2001 Elsevier Science Ltd. All rights reserved.