STRUCTURE-FUNCTION RELATIONSHIP OF HYPERTHERMOPHILIC ENZYMES

The upper limit of thermal adaptation in the biosphere (almost-equal-to 110-degrees-C) coincides with the temperature where hydrophobic hydration vanishes and biomolecules start undergoing hydrothermal decomposition. Regarding T(max), hyperthermophilic microorganisms come close to this limit. Thermotoga maritima (T(opt) less-than-or-equal-to 90-degrees-C) has adapted its cellular inventory to T greater-than-or-equal-to 100-degrees-C. Enzymes purified to homogeneity show intrinsic stability up to almost-equal-to 110-degrees-C. Their overall properties at physiological temperature resemble those of their mesophilic counterparts: Mutative adaptation tends to maintain ''corresponding states'' regarding structure, flexibility and ligand binding. Physical, enzymatic and folding properties of glyceraldehyde-3-phosphate dehydrogenase, lactate dehydrogenase and amylase are discussed. Enhanced stability may be ascribed to improved packing and enhanced ligand and/or subunit interactions. Due to the minute adaptive changes in DELTAG no general strategy of thermophilism can be given.