Cryotoxic solutes

Figure 3. Inactivation of thylakoids during freezing at various low temperatures as a function of time. Washed thylakoids were suspended in a solution containing 50 mM sucrose as a cryoprotectant and 20 mM sodium phenylpyru-vate as a cryotoxic solute. The suspensions were rapidly frozen and thawed. After thawing, photophosphorylation was determined. For experimental conditions, see notes in legend for Fig. 2...

Colligative Protection. The principles of colligative protection were first outlined by Lovelock (35) for the red blood cell. These principles are also valid for the thylakoid system (14,21,68). If only one solute is present in a membrane suspension, its concentration, regardless of its initial concentration, will rise dining freezing to a level determined solely by the final freezing temperature. If the solute is a cryotoxic compound, this final level may be sufficient to cause membrane inactivation. When several solutes are present and only one is a cryotoxic solute, the same... 

CryoPROTEcnvE Proteins. In general, soluble proteins are either weakly effective or ineffective for preventing the freeze-inactivation of thylakoids suspended in dilute salt solutions. This is not unexpected since low concentrations of high molecular weight compounds such as proteins cannot significantly reduce the freeze-concentration of cryotoxic solutes by colligative action. However, some proteins extracted from frost-... 

Protection of thylakoids by large molecules might be explained in several ways. Perhaps the thylakoid membrane is sensitive to solute injury only on the outer side, or the intrathylakoid space contains, even after long incubation, little of the added cryotoxic solute, or penetration of the membrane by normally nonpenetrating solutes becomes possible under freezing conditions (76). 

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