Succinate dehydrogenase (SDH, E.C, 1.3.5.1) consists of 4 subunts (SDHA, SDHB, SDHC, SDHD) and converts s to fumarate within the Krebs cycle (also known as Tricarboxylic acid cycle or citric acid cycle). Here we designed an assay which follows a colorimetric marker's color chain as FADH2 is created. We use the kinetic mode on our xMark™ Microplate Absorbance Spectrophotometer (Bio-Rad).