7-Methyl-6-thioguanosine

7-Methyl-6-thioguanosine (MESG) is a chromogenic substrate that can be converted to 7-methyl-6-thioguanine in the presence of purine nucleoside phosphorylase and inorganic phosphate. 7-Methyl-6-thioguanosine can be used to quantify inorganic phosphate. 7-Methyl-6-thioguanosine can also be used to determine the activities of purine nucleoside phosphorylase and protein phosphatases^[1][2]. In Vitro:Brief Steps for Assaying Protein Phosphatases^[1]:
1. Reagent Preparation: Prepare a stock solution of 7-Methyl-6-thioguanosine in DMSO for use on the same day. Determine its concentration based on the absorbance value at 331 nm and the corresponding molar extinction coefficient.
2. Reaction System Setup: Prepare the reaction mixture according to the type of protein phosphatase to be detected.
3. Reaction Detection: Equilibrate the reaction mixture at 25°C for 5 minutes, then add the protein phosphatase to initiate the reaction. Record the absorbance changes at 360 nm using a double-beam spectrophotometer. Determine the initial reaction rate by analyzing the slope of the reaction curve with software, and quantify the released phosphate based on a specific extinction coefficient.
4. Data Analysis: Process the data using a non-linear regression analysis program, calculate parameters such as K_m, V_max to evaluate the activity of the protein phosphatase.