Abstract:Succinate dehydrogenase (SDH) was purified by DEAE C-32 chromatography from the mitochondrial fraction of corn ( Zea mays L. ). Free calmodulin (CAM) could not be detected in the purified SDH with the method based on the ability of SDH to stimulate NAD kinase, but it still contained some CAM when measured with the ELISA method. Purified SDH could stimulate NAD kinase only after heating to release free CAM. Plain polyacrylamide gel electrophoresis (PAGE) of the pufffled SDH revealed only one peptide band, but three peptide bands were shown on SDS-PAGE, their molecular weight being 67.0 kD, 30.0 kD, 16.7 kD respectively. The 67.0 kD and 30.0 kD peptides corresponded to the large and small molecular subunit of SDH respectively. The Rf value of the 16.7 kD peptide band was identical to the standard CAM in the SDS-PAGE. From all the above evidence, the authors suggested that CAM might exert its function of SDH regulation in a binding state with the SDH molecule.