An improved method to determine the molecular weight of the subunit of lactate dehydrogenase and malate dehydrogenase after sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) has been developed. This method was based on the finding that on a gel, which was washed with a buffer to remove SDS after SDS-PAGE, stained with an enzymatic activity staining mixture and then stained with coomassie blue, there appeared one active stained band with apparent molecular weights of 35,500 (monomer) (lactate dehydrogenase) and 31,000 (monomer) (malate dehydrogenase) on the SDS-PAGE gel. The method developed here may be applicable to a wide range of active stainable-enzymes as a rapid and simple molecular weight determination method of the subunit after SDS-PAGE
