Both stability and catalytic activity of the HynSL Thiocapsa roseopersicina hydrogenase in the presence of different water-miscible organic solvents were investigated. For all organic solvents under study the substantial raise in hydrogenase catalytic activity was observed. The stimulating effect of acetone and acetonitrile oil the reaction rate rose with the increase ill solvent concentration up to 80%. At certain concentrations of acetonitrile and acetone (60-80%, v/v in buffer solution) the enzyme activity was improved even 4-5 times compared to pure aqueous buffer. Other solvents (aliphatic alcohols, dimethylsulfoxide and tetrahydrofuran) improved the enzyme activity at low concentrations and Caused enzyme inactivation at intermediate concentrations. The long-term incubation of the hydrogenase with aliphatic alcohols, dimethylsulfoxide and tetrahydrofuran at intermediate concentrations of the latter caused enzyme inactivation. The reduced form of hydrogenase was found to be much more sensitive to action of these organic solvents than the enzyme being in oxidized state. The hydrogenase is rather stable at high concentrations of acetone or acetonitrile during long-term storage: its residual activity after incubation in these solvents upon air within 30 clays was about 50%, and immobilized enzyme remained at the 100% of its activity during this period. (C) 2008 Elsevier Inc. All rights reserved.