The Osmotic Inactivationin situof Plant Mitochondrial Enzymes

Abstract

When cauliflower buds are gently disrupted in distilled water and homogenized immediately thereafter in hypertonic sucrose, the succinoxidase activity of par ticles prepared from such homogenates is considerably less than that of particles prepared from tissue homogenized in sucrose directly. Other enzymatic functions are impaired as well. When tissue is washed in water for any length of time prior to homogenization, the deleterious effect of hypotonicity is exaggerated. The irreversible injury to the mitochondria brought about by a hypotonic environment may be precluded to some extent by maintaining the temperature at o° C. Wash ing injury is also minimized by washing tissue in hypertonic solutions. In addition to the irreversible osmotic injury which the mitochondria may undergo, a reversible inhibition of succinic dehydrogenase may be effected by a soluble, heat-stable component of cauliflower juice. The latter inhibition appears to be competitive in nature. The reduction of ferricyanide has been used as a means of measuring succinic dehydrogenase activity anaerobically. The concordance of manometric and potentiometric measurements of dehydrogenase activity suggests that the ferro cyanide ion may move freely from within the cell to the outer solution. There are indications as well that certain endogenous cell materials may be removed from the tissue during relatively short washing-periods.