Some properties of mitochondria, mitoplasts and submitochondrial particles of different polarities from plant tissues

Abstract

Irrespective of the starting material, i.e. washed mitochondria, purified mitochondria or mitoplast from Solanum tuberosum L., submitochondrial particles of well-defined polarities can be generated by French press treatment in low-salt medium or by sonication in high-salt medium. The first treatment will result in submitochondrial particles which are more than 80% right-side-out (right-side-out particles), the second in submitochondrial particles that are more than 80% inside-out (inside-out particles). The isoelectric point (p I = 4.0) of the inside-out particles measured by cross-partition is distinctly different from the isoelectric points of the other mitochondrial membranes which exhibit p I values between 4.5 and 4.7. The surface charge density measured by 9-aminoacridine fluorescence varies in the same order from −27 mC · m −2 for Percoll-purified mitochondria to −51 mC · m −2 for both right-side-out and inside-out particles. Even though the charge densities for the two surfaces of the inner membrane are similar, inside-out particles are much more negatively charged at pH 7.0, since they are 6-times larger. These results clearly demonstrate that it is possible to obtain submitochondrial particles of various polarities and sizes which in turn constitute valuable tools for the study of lateral and transverse asymmetry of the inner mitochondrial membrane.