Biophys J, August 2000, p. 1119-1128, Vol. 79, No. 2

High Critical Temperature above T_g May Contribute to the Stability of Biological Systems

Julia Buitink,^* Ivon J. van den Dries, Folkert A. Hoekstra,^* Mark Alberda,^* and Marcus A. Hemminga

Wageningen University,  ^*Department of Plant Sciences, Laboratory of Plant Physiology, 6703 BD Wageningen,  Department of Biomolecular Sciences, Laboratory of Molecular Physics, 6703 HA Wageningen, and  Department of Food Science, Food Physics Group, 6703 HD Wageningen, The Netherlands

In this study, we characterized the molecular mobility around T_g in sugars, poly-L-lysine and dry desiccation-tolerant biological systems, using ST-EPR, ¹H-NMR, and FTIR spectroscopy, to understand the nature and composition of biological glasses. Two distinct changes in the temperature dependence of the rotational correlation time (_R) of the spin probe 3-carboxy-proxyl or the second moment (M₂) were measured in sugars and poly-L-lysine. With heating, the first change was associated with the melting of the glassy state (T_g). The second change (T_c), at which _R abruptly decreased over several orders of magnitude, was found to correspond with the so-called cross-over temperature, where the dynamics changed from solid-like to liquid-like. The temperature interval between T_g and T_c increased in the order of sucrose < trehalose < raffinose  staychose < poly-L-lysine < biological tissues, from 17 to >50°C, implying that the stability above T_g improved in the same order. These differences in temperature-dependent mobilities above T_g suggest that proteins rather than sugars play an important role in the intracellular glass formation. The exceptionally high T_c of intracellular glasses is expected to provide excellent long-term stability to dry organisms, maintaining a slow molecular motion in the cytoplasm even at temperatures far above T_g.

Biophys J, August 2000, p. 1119-1128, Vol. 79, No. 2
© 2000 by the Biophysical Society   0006-3495/00/08/1119/10  $2.00

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