The effect of ribonuclease on oxidative phosphorylation by mitochondria.

In current studies in this laboratory on the composition and activity of plant mitochondria as a function of growth, it has been noted that well washed mitochondrial preparations contain about 1 per cent of the dry weight as ribonucleic acid. Most of this RNA may be due to microsomal contamination, for electron micrographs show corn mitochondrial preparations to be quite heterogeneous (1). However, the possibility remains that some RNA may be a constitutive part of the mitochondrion proper and may even have a functional role in phosphorylation. Pinchat (2, 3) has reported a polynucleotide requirement for oxidative phosphorylation by extracts of the bacterium Alcaligenes fuecalis, and Allfrey and Mirksy (4, 5) have found polynucleotides or polyanions necessary for ATP formation in thymus nuclei. Lowe and Lehninger (6), on the other hand, have demonstrated that highly polymerized RNA is not essential to phosphorylation by liver mitochondria. It appeared that the simplest means of determining whether plant mitochondria contain a polynucleotide moiety functional in oxidative phosphorylation would be to treat the mitochondria with ribonuclease. If RNase penetrates plant membranes, as is suggested by the inhibitions the enzyme produces on salt uptake (7) and protein synthesis (8, 9) when applied to roots, RNA in the mitochondrion or mitochondrial membrane should be accessible for degradation. Zollinger (10) observed in the phase contrast microscope that RNase-treated mitochondria suffered some internal dispersion on secondary swelling in water. Although RNase has been reported to have no effect on phosphorylation in bacterial extracts (2), respiration in roots (8), and succinoxidase activity in liver mitochondria (II), it was decided to study the effect of RNase on plant mitochondria. The experiments showed that RNase markedly impairs oxidative phosphorylation in corn and soybean mitochondria; the same effect was obtained with rat liver mitochondria.