Comparative studies on the thermophilicity and stability of 5′-methylthioadenosine phosphorylase from various sources

Abstract 5′-Methylthioadenosine (MTA) phosphorylase, isolated from a number of mesophilic, moderately thermophilic, thermophilic and hyperthermophilic organisms shows unique features of thermophilicity and thermostability with an optimum temperature ranging from 60°C (rat liver) and 125°C ( Pyrococcus furiosus ) and an apparent Tm ranging from 60°C (rat liver) and 140°C ( Pyrococcus furiosus ). The enzyme appears not only exceptionally thermostable, but also stable in the presence of organic solvents, protein denaturants and detergents. As far as the resistance to proteolysis, MTA phosphorylase from extremely thermophilic and hyperthermophilic microorganisms are completely resistant to the degradation by trypsin, chimotrypsin and thermolysin. MTA phosphorylase from various sources is characterized by different molecular weights, ranging from 66000 to 155000. Unlike mammalian MTA phosphorylase, the homologous enzyme from thermophilic sources does not require reducing agents for catalytic activity.