Abstract: Kinases can be engineered to utilize an ATP analog that is not readily utilized by wild-type kinases by introducing a mutation in the ATP-binding pocket. However, application of this method has been limited by the membrane impermeability of the ATP analog. Provided herein are methods for in situ visualization of substrates of an analog-sensitive kinase, the method comprising a mild fixation step. Also provided herein are kits comprising a fixative, an ATP analog, and an agent for detecting the substrates modified by the ATP analog.