Abstract:The mung bean mitochondria were obtained by sucrose cushion centrifugation in quite pure form. The outer membrane and the mitoplast were separated by digitonin treatment followed by sucrose density gradient centrifugation. SDS gradient polyacrylamide gel electrophoresis showed that the 42–44 KD protein in mung bean mitochondria was located in mitoplast rather than in the outer membrane. Co-electrophoresis with rabbit muscle actin showed that the rabbit muscle actin coincided with the 44 KD band in plant mitochondria. These results suggest that one of the motive force of the swelling and shrinking of the mitochondria may be generated from the mitochondria themselves.