PubMed · 1098674
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L Bachmann. 1975. Proceedings: Developments in cryofixation.. https://pubmed.ncbi.nlm.nih.gov/1098674/
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A wide variety of compounds, including sugars, polyols, amino acids and certain salts, are effective at minimizing protein denaturation during freeze-thawing. In this review we provide evidence that the mechanistic basis for this cryoprotection appears to be the same as that described by Timasheff for solute-induced stabilization in aqueous solution. Namely, the stabilizers are preferentially excluded from the surface of the protein, and this interaction makes it thermodynamically unfavourable for proteins to unfold. In contrast, carbohydrate-induced preservation of labile enzymes during freeze-drying is a fundamentally different process. Using Fourier transform intra-red spectroscopy we have found that hydrogen bonding between the carbohydrate and the dried protein is required for stabilization. Thus, it appears that certain carbohydrates protect dried enzymes because these solutes serve as water substitutes for the dried protein, by satisfying the hydrogen bonding requirement of polar groups on the protein's surface. Finally, we discuss some intriguing findings on the synergistic stabilization of proteins by mixtures of divalent cations and organic solutes, which are yet to be explained.
The alterations of the amount of hydration water and the extent of the interaction with hydration water and protein during freezing and after freeze-drying were investigated with or without cryoprotectant using 1HNMR and other methods. Ovalbumin was used as a representative protein that was stable against freezing and drying. Myosin was also used as a typical unstable protein. It was found that myosin had no stable hydration layer compared with ovalbumin. It was considered that this difference might be the major cause of the difference in the stability of both proteins against freezing and drying. With cryoprotectant, the amount of hydration water was decreased and the extent of the interaction of hydration water with protein was increased. The results suggested the effective protectant substituted for part of the hydration water and strengthened the interaction during freezing and drying. It is also possible that the formation of a "quasi-hydration layer" might protect protein against denaturation due to freezing and drying.
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