THE INFLUENCE OF SUGARS ON THE PROPERTIES OF FREEZE-DRIED LYSOZYME AND HEMOGLOBIN

To learn more about the role of the sugar trehalose in anhydrobiosis, a study has been made of the effect dehydration has on properties of the proteins Lysozyme and haemoglobin. Solutions containing just the proteins or the proteins and a sugar, either trehalose, galactose or glucose, were freeze dried. Differential scanning calorimetry of Lysozyme showed that in going from dilute solution to the solid state the denaturation temperature increased by 70 °C and the denaturation enthalpy change halved. Unlike solutions where addition of sugar caused an increase in denaturation temperature (Td), in the dry state the presence of sugar reduced Td The denaturation enthalpy changes in the presence of sugars ranged from values similar to those measured in dilute solution to values almost three times greater. Dehydration of oxyhaemoglobin solutions in the absence of sugars led to oxidation of the haem group and the formation of methaemoglobin. The presence of sugars either completely suppressed or markedly reduced haem oxidation during dehydration and reduced the oxidation rate when dry haemoglobin was stored. These results show that sugars can substitute for water and so enable proteins to retain in the solid state properties they usually exhibit only in aqueous solution. Two factors have been identified which may make trehalose of special value to anhydrobiotic organisms. Trehalose does not react with proteins at elevated temperatures, as reducing sugars do, and its solutions are more readily dehydrated.