5-methylthioribose 1-phosphate: a product of partially purified, rat liver 5'-methylthioadenosine phosphorylase activity.

5'-Methylthioadenosine phosphorylase from rat liver has been purified 112-fold. A molecular weight of 90 000 for the enzyme was estimated from gel filtration on Sephadex G-150. The Km for 5'-methylthioadenosine was 4.7 . 10(-7) M, while the Km for phosphate was 2 . 10(-4) M. The products of the reaction were isolated and identified as adenine and 5-methylthioribose 1-phosphate. In addition to 5'-methylthioadenosine the nucleoside analogues 5'-ethylthioadenosine and 5'-n-propylthioadenosine also served as substrates for the enzyme. The 7-deaza analogue 5'-methylthiotubercidin was found to be an inhibitor of the reaction, but was inactive as a substrate.