Kinetic properties and the effect of substrate analogues on 5′-methylthioadenosine nucleosidase from Escherichia coli

Abstract

5′-Methylthioadenosine nucleosidase (EC 3.2.2.-) from Escherichia coli has been purified 220-fold. A molecular weight of 31 000 for the enzyme was estimated from gel filtration on Sephadex G-150. The K m for 5′-methylthioadenosine was 3.1 · 10 −7 M. In addition to 5′-methylthioadenosine, the nucleoside analogues 5′-ethylthioadenosine, 5′-n- propylthioadenosine , and S- adenosylhomocysteine also served as substrates for the enzyme. These substrate analogues acted as competitive inhibitors of the reaction with 5′-methylthioadenosine. The K i values for 5′-ethylthioadenosine, 5′-n- propylthioadenosine , and S- adenosylhomocysteine were determined to be 1.3 · 10 −7 M, 4.6 · 10 −8 M, and 1.92 · 10 −7 M respectively.