Effect of Phospholipases and Lipase on Submitochondrial Particles

Abstract 1. Exposure of submitochondrial particles to phospholipases impaired the rate of oxidation as well as phosphorylation. Phospholipase A and phospholipase C were more inhibitory to phosphorylation and to NADH oxidation than to succinate oxidation. 2. At low concentrations of phospholipase A the inhibition of phosphorylation was prevented to a considerable extent by the presence of large amounts of bovine serum albumin preferably during both digestion and assay. At larger concentrations of phospholipase A only slight protection was observed by addition of serum albumin. 3. Exposure of submitochondrial particles to phospholipase C from Clostridium welchii in the presence of Mg++ or Mn++ inhibited the 32Pi-ATP exchange and the P:O ratio by about 30 to 60%. Addition of coupling factors restored phosphorylation associated with oxidation in these particles. Additional exposure of the digested particles to phospholipase C from Bacillus cereus in the presence of Zn++ further depressed the 32Pi-ATP exchange which was no longer restored by coupling factors. Addition of phospholipids partially restored the 32Pi-ATP exchange in these extensively digested particles. Similar effects were noted after prolonged exposure to phospholipase C from B. cereus alone, provided both Mn++ and Zn++ were present. 4. Oxidative phosphorylation was also severely impaired after exposure of submitochondrial particles to phospholipase C from B. cereus in the presence of Mn++ and Zn++. A partial restoration of the P:O ratio was achieved by reconstitution with phospholipids.