In this chapter, we describe a method to extract and quantify photosynthetic enzymes using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. The method is particularly suitable for characterizing altered protein amounts in leaves of plants produced from genetic engineering or gene editing approaches. We focus on Rubisco and Rubisco activase, a molecular chaperone required to sustain the activity of Rubisco and CO2 fixation, yet the method can be easily adapted to investigate other leaf proteins of interest.