[Inhibition of respiratory enzymes in mitochondria of green leaves]

1. Of the buffer substances introduced by Good, only N-2-hydroxy-ethylpiperazine-N-2-ethanesulfonic acid (HEPES) and N-tris(hydroxymethyl)-methyl-2-aminoethanesulfonic acid (TES) were found suitable for the isolation of mitochondria by means of density gradient centrifugation in a silica sol. Addition of 1% polyvinylpyrrolidone remarkably reduced the respiration rate and diminished the respiratory control, whereas 2% dextran improved the rates. 2. Fifty mM malonate inhibited succinate oxidation by 55-72% compared with the controls; in addition an uncoupling effect was observed. Similar results were obtained with 2.5 mM amytal. 3. Antimycin A, in contrast, did not affect the respiratory control, while the respiration rate was depressed to 55% of that in the control. 4. Azide (20 mM) had only a slight effect on the two parameters of leaf mitochondria. 5. It can be concluded that mitochondria of leaf cells are provided with the same respiratory enzymes as those of other plant materials.