S-ADENOSYLHOMOCYSTEINE HYDROLASE FROM THE THERMOPHILIC ARCHAEON SULFOLOBUS-SOLFATARICUS - PURIFICATION, PHYSICOCHEMICAL AND IMMUNOLOGICAL PROPERTIES

S-Adenosylhomocysteine hydrolase from Sulfolobus solfataricus, a therm oacidophilic archaeon optimally growing at 87-degrees-C, has been puri fied to homogeneity. The specific activity of the homogeneous enzyme i s 161 nmol of S-adenosylhomocysteine formed per min per mg of protein, and the overall yield, by immunoaffinity purification, is 51%. The en zyme has a molecular mass of 190 kDa, is composed of four identical su bunits (subunit mass 47 kDa), and contains four molecules of tightly-b ound NAD+ per tetramer of which about 40% is in the reduced form. Phys ico-chemical features, including amino-acid composition and secondary structure, are reported. The pure protein, used to raise specific rabb it antisera, shows immunological properties different from other S-ade nosylhomocysteine-metabolizing enzymes. The enzyme is thermophilic wit h an optimum temperature of 75-degrees-C, and shows an apparent meltin g temperature of 95-degrees-C by measuring its residual activity after 10 min incubation at increasing temperatures.