Studies on stability of S-adenosylhomocysteine hydrolase from Sulfolobus solfataricus, a thermophilic archaebacterium

Abstract S-adenosylhomocysteine hydrolase from Sulfolobus solfataricus , a thermoacidophilic archaebacterium, exhibits a maximum activity at 75°C and shows a biphasic Arrhenius plot. The thermostability of the enzyme is notably high; in fact, S-adenosylhomocysteine hydrolase is completely stable after 16 hours preincubation at 50°C, retains 60% of initial activity at 70°C, and shows a half-inactivation time of 130 min at 90° C and of 40 min at 100°C. Values of residual activity after 10 min incubation at increasing temperatures allow the determination of an apparent melting temperature of 104°C. Moreover, after 24 hours of preincubation at room temperature, no loss of enzymatic activity is detected in the presence of 6M urea, 6M guanidine hydrochloride and 0.05% SDS. Furthermore, about 90% and 95% of initial activity was retained in the presence of 50% methanol and 50% ethanol respectively. Data are also reported on the enzyme's resistance to proteolysis and on the effect of salts, detergents, denaturants, and organic solvents on thermostability.