Table 3.

Comparison of the ΔG stab-versus-T curves for some mesophile, thermophile, and hyperthermophile proteins

Thermophilic/mesophilic source (reference)ProteinCharacteristics ofΔG-vs-T curve for thermophilic enzyme, ΔGa (kcal/mol)
Thermus thermophilus/E. coli(142)RNase HΔG-vs-T curve shifted toward higher ΔGs and flattened
Bacillus stearothermophilus/yeast(79)PGKΔG-vs-T curve probably shifted toward higher ΔGs ΔΔGb = 5 kcal/mol at 20°C
T. thermophilus/yeast (265)PGKΔG-vs-T curve shifted toward higher ΔGs and flattened (smaller ΔCp)
T. thermophilus: ΔG = 6.32 kcal/mol at 25°C; yeast: ΔG = 3.63 kcal/mol at 25°C
T. thermophilus/horse (264)Cytochromec-552ΔG-vs-T curve shifted toward higher ΔGs and higher temperatures
T. thermophilus: ΔG = 28.5 kcal/mol at 25°C; horse: ΔG = 12.7 kcal/mol at 25°C
Sulfolobus acidocaldarius/assortment of mesophilic proteins (241)Sac7d DNA binding proteinΔG-vs-T curve flattened
T. maritima/E. coli (76)Dihydrofolate reductaseΔG-vs-T curve shifted toward higher ΔGs and higher temperatures
T. maritima/yeast (121)PGKΔG-vs-Tcurve shifted toward higher ΔGs
T. maritima: ΔG max c = 28.7 kcal/mol at 30°C; yeast: ΔG max = 6.0 kcal/mol at 30°C
T. maritima/bovine adrenal cortex FerredoxinΔG-vs-T curve shifted toward higher ΔGs and higher temperatures
 (274) T. maritima: ΔG max = 9.3 kcal/mol at 45°C; bovine: ΔG max = 4.8 kcal/mol at 25°C
P. furiosus and M. fervidus (a and b)/M. formicicum(216)HistoneΔG-vs-T curve shifted toward higher ΔGs and higher temperaturesP. furiosus: ΔG max = 17.2 kcal/mol at 44°C (Tm = 114°C); M. fervidus a: ΔG max = 15.5 kcal/mol at 35°C (Tm = 104°C), M. fervidus b: ΔG max = 14.6 kcal/mol at 40°C (Tm = 113°C), M. formicicum: ΔG max = 7.2 kcal/mol at 32°C (Tm = 75°C)
P. furiosus/mesophilic proteins inRubredoxinΔG-vs-T curve shifted toward higher ΔGs and higher temperatures
 general (141)ΔG max = 18 kcal/mol at 65°C (Tm = 176–195°C)
S. solfataricus/pig (14)AspartateΔG-vs-T curve flattened (smaller ΔCp ) and probably shifted toward higher ΔGs
 aminotransferase S. solfataricus: ΔG = 16.8 kcal/mol at 25°C; pig: ΔG = 13.8 kcal/mol at 25°C
  • a ΔG, ΔG stab.

  • b ΔΔG, difference in ΔG stab between the thermophilic and mesophilic enzymes.

  • c ΔG max, maximal ΔG stab.