5-Methylthioribose kinase. A new enzyme involved in the formation of methionine from 5-methylthioribose.

The presence of a previously unidentified enzyme, tentatively designated 5-methylthioribose kinase, has been demonstrated in cell-free extracts of Enterobacter aerogenes. The enzyme catalyzes the ATP-dependent phosphorylation of 5-methylthioribose. ADP is one of the products of the reaction and, based on functional group analyses, the other product is 5-methylthioribose 1-phosphate. A 40-fold purified enzyme preparation has been obtained from a cell-free extract of E. aerogenes. Activity of the partially purified enzyme is totally dependent on the presence of a divalent cation and a sulfhydryl reagent. The substrate specificity of the enzyme is quite narrow, and the Km values for ATP and 5-methylthioribose are 7.4 X 10(-5) M and 8.1 X 10(-6) M, respectively. These results suggest that 5-methylthioribose kinase may be a primary enzyme involved in the recycling of the methylthio group of 5-methylthioribose back into methionine.