Comparative effects of purified staphylococcal alpha and delta toxins on mitochondrial metabolism.

Abstract

Purified staphylococcal alpha toxin, free of delta-toxin activity, was prepared by ammonium-sulfate precipitation followed by chromatography on diethylaminoethyl- and carboxymethylcellulose and Sephadex G-100. Unlike delta toxin, alpha toxin was not inhibited by phospholipids and had no effect on mitochondria of the rat or rabbit liver. Delta toxin caused mitochondrial lysis with inhibition of respiration and phosphorylation. However, in the presence of succinate and cytochrome c, respiration was stimulated, suggesting an intact electron-transport system, except for loss of functional cytochrome c. Magnesium-dependent, mitochondrial adenosine triphosphatase was stimulated by delta toxin. Neither alpha nor delta toxin had activity of phospholipase A, C, or D. The action of delta toxin on mitochondria is similar to that of the detergents Triton X-100 and deoxycholate. Purified staphylococcal alpha toxin was previously shown to inhibit active transport of sodium, to stimulate consumption of oxygen, and to increase activity of magnesium-dependent adenosinetriphosphatase (ATPase) in the isolated bladder of the toad [1]. These findings led to an investigation of the action of alpha toxin on energy-producing reactions of isolated mitochondria. The ratio of phosphorus to oxygen was reduced in mitochondrial preparations from the rabbit liver that were exposed to alpha toxin, and the activity of magnesium-dependent mitochondrial ATPase was enhanced, suggesting uncoupling of oxidative phosphorylation [2]. Further studies on the action of alpha toxin on mitochondrial metabolism were undertaken with toxin prepared as before by ammonium-sulfate precipitation and ion-exchange chromatography. However, Sephadex molecular-sieve chromatography was used rather than paper-curtain electrophoresis. The experiments reported in this paper were done with both alpha and delta toxin in parallel and indicate that the previously described effects of alpha toxin on mitochondrial structure and function are due to delta toxin. The nature of these effects has thus