There is plenty of alternate oxidase (AOX) in the inflorescences of thermogenic A rum maculatum. The isolated mitochondria exhibited a high activity, consuming oxygen on average 32 micromoles/min. The concentration of the isolated protein from mitochondria was 14.0 mg/ml. The isolated mitochondria were crashed by osmotic method to isolate matrix, membrane, and membrane soluble and insoluble proteins. The whole mitochondria, membrane and membrane soluble protein showed AOX activity while the matrix and membrane insoluble protein did not displayed AOX activity. The proteins were purified with FPLC by adding deoxycholamide dBC. The purified enzyme fraction exhibited a high specific activity, which could be kept for at least 6 months when stored at -70 degrees C. Furthermore, we used a silver stain system to identify the AOX, which showed 4 different protein bands from 30 kD to 32 kD. 2-dimensional electrophoresis showed 4 isoelectric points in the range from pH6.4 to 7.4 respectively.