7-methyl-6-Thioguanosine is a chromophoric substrate that is used to quantify inorganic phosphate (Pi). In the presence of purine nucleoside phosphorylase, it reacts with Pi to produce 7-methyl-6-thioguanine and ribose 1-phosphate, with the increase in 7-methyl-6-thioguanine followed by continuous spectrophotometry at an absorbance of 355-360 nm. 7-methyl-6-Thioguanosine is also used to measure changes in Pi levels in coupled enzyme systems, including assays of the activities of protein phosphatases, phosphorylase kinases, GTPases, and ATPases.
