Cryoprotective effect of glycine betaine and glycerol is not based on a single mechanism.

The mechanism of action of the osmoregulatory substances glycine betaine and glycerol in the course of the freeze-thaw cycle was studied. Photochemical activity of isolated thylakoid membranes was effectively protected during freezing by both solutes by preventing dissociation of the peripheral cold labile proteins - the water splitting system and plastocyanin. It is suggested that the cryoprotective effect of glycine betaine and glycerol is based on a mechanism similar to the well documented stabilization of complex enzymes against dissociation into subunits at high salt concentrations. Specific solute-membrane interactions additionally contribute to the observed cryoprotective effect. The binding of the molecules of glycine betaine and glycerol is limited to the water lipid interface of thylakoid membranes.