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Previous studies have demonstrated that the phospholipase A from cobra venom can uncouple oxidative phosphorylation in brain and liver mitochondria (Aravindakshan & Braganca, 1959). These effects had been observed both in experiments in vitro as well as in animals injected with the material. Comparative studies carried out with animals injected with crude cobra venom and with heated venom (phospholipase A) had shown that heated venom could not lower the P:O ratio in the intact animal to less than 1-5, even if the animals were injected with large quantities of the material or killed after longer intervals of time. It is well established that three molecules of adenosine triphosphafe are formed during the transfer of electrons from diphosphopyridine nucleotide-linked substrates to oxygen. The three phosphorylations are known to occur in steps in different regions of the respiratory chain (Chance & Williams, 1956). It was therefore of interest to explore whether the partial uncoupling of oxidative phosphorylation observed in animals injected with preparations containing phospholipase A was confined to a particular site. Experiments in vitro designed to localize the site of activity of some other uncoupling agents have shown that gramicidin (Lehninger, 1954-55) and salicylate (Penniall, 1958) preferentially inhibit the phosphorylation in the region of cytochrome c-oxygen. The effect of thyroxine has been investigated in the intact animal by Maley & Lardy (1955), and the data show that thyroxine is equally effective in uncoupling the various phosphorylation steps. The evidence described in this paper demonstrates that phospholipase A (heated venom) can preferentially uncouple the phosphorylation coupled to cytochrome oxidase when added to isolated brain or liver mitochondria as well as in animals injected with the substance. Apparently in the intact animal the phospholipids associated with phosphorylation in the region of reduced diphosphopyridine nucleotide-cytochrome c are not easily attacked by phospholipase A.

Preferential inhibition of phosphorylation in different parts of the respiratory chain in mitochondria obtained from animals injected with cobra venom