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 -n-glucan: scleroglucan (1.0 mg/ml), w as investigated using HPLC and electron microscopy. The fraction of cyclic (C) and linear (L) topologies of the samples renatured from alkaline soluti on when [NaOH] was 0.35 M or higher, remained in most cases constant follow ing storage in neutral aqueous solution for 18 months at room temperature. Electron microscopy revealed a reduction of C and increase of L following t he long-term storage for scleroglucan renatured from [NaOH] less than 0.25 M. Annealing of renatured samples at temperature T-a equal 100 degreesC gav e rise to a stable distribution of 60% cyclic and 13% linear topologies. In creasing T-a above 100 degreesC yielded a distribution of topologies that r educed in initial cyclic fraction from 17% to 5 +/- 3% for T-a = 133 degree sC following the 18 months storage. These changes in the distribution of to pologies manifested itself also in changes in the HPLC elution profiles. In particular, the solvent history producing long-term structurally stable di stribution of species of the annealed sample (T-a = 100 degreesC) also yiel ded unchanged HPLC elution profiles. Our data suggest that rearrangements o f 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 E lsevier Science Ltd. All rights reserved.