An electrophoretic study of suspensions of intact mitochondria and fragments of mitochondrial membranes

The electrophoretic properties of rat-liver mitochondria and mitochondrial membrane fragments produced by sonic disruption have been studied in the pH interval 6.5 to 7.9, using free boundary electrophoresis. The limiting membrane of the intact mitochondrion has been found to bear a net negative charge of 2.7–3.7·10 3 esu cm −2. It is apparent that there are no titratable groups with a p K in the range of 6.5–7.9 on the mitochodrrial surface. Evidence is presented which indicates that the anion HPO 4 = is bound by the mitochondrial surface. An investigation of the electrophoretic mobility as a function of the degree of motochondrial swelling, which shows that there is no significant change in the charge density per unit area, suggests that the large increase in surface area associated with swelling does not occur by a “stretching” process. A comparison of the electrophoretic behavior of intact mitochondria and sonic membrane fragments indicates that the electrokinetic surface of shear is not the same in these two preparations.