A new and highly sensitive assay for the ATP phosphoribosyltransferase that catalyzes the first step of histidine biosynthesis

A new method is described for assaying the ATP phosphoribosyltransferase (EC 2.4.2.17) that catalyzes the first step of histidine biosynthesis in bacterial cells. This is a highly sensitive radioassay, capable of detecting fewer than 10 9 molecules of enzyme. In contrast to the previously available assay, it can be carried out in the presence of other molecules that absorb uv light. The assay may find useful application in studies on the in vitro synthesis of the enzymes for histidine biosynthesis and in studies on the various aggregation states of the enzyme.