Concentrated and partially purified preparations of streptococcal supernates containing streptolysin O have been shown to inhibit selectively the oxidative metabolism of mitochondria procured from the myocardium of rabbits and guinea pigs, the findings pointing to an interference with the action of the coenzyme diphosphopyridine nucleotide (DPN) (1). Further studies have demonstrated that these streptococcal preparations contain an enzyme, not hitherto discerned in streptococcal cultures, that specifically destroys DPN. Some of the characteristics of this enzyme, and its separation from streptolysin O, will be described in detail herein. Materials and MethodsThe ability of streptococcal preparations to destroy DPN in vitro was determined under various conditions of temperature, pH, and enzyme concentration, using the assay procedure for diphosphopyridine nucleotidase (DPNase) described by Kaplan, Colowick, and Nason (2). In other experiments, the separation of streptolysin O from the agent destroying DPN was attempted by means of electrophoretic fractionation. In still other experiments, the specificity of the agent for DPN and the precise site of cleavage of the DPN molecule were investigated.Streptococcal Preparations.--Most of the experiments to be described were carried out with fractionated culture supernates prepared from 15 liter cultures of the C203S strain of group A streptococcus according to the method previously described (3). The solutions were dialyzed

Infections with group A streptococci are considered to be responsible for the development of important structural and functional changes in the hearts of human beings and experimental animals (1, 2), but the manner in which streptococcal infections bring about these changes remains obscure. Of the diverse extracellular products elaborated during the growth of group A streptococci, only two---streptococcal proteinase and streptolysin O--are known to have an effect upon the heart. A single intravenous injection of crystalline streptococcal proteinase has been shown to cause focal necrosis of the myocardium in rabbits, mice, and guinea pigs (3); and solutions containing streptolysin O have been found to induce systolic contracture of the isolated frog heart (4-6). The studies now to be presented demonstrate that a minute quantity of streptolysin O brings about a prompt and irreversible loss of myocardial contractile power when per[used through the isolated hearts of guinea pigs, rabbits, and rats. Materials and MethodsThe general plan of the experiments was as follows. Hearts were removed from guinea pigs, rabbits, and rats, set up in a modified Langendorff apparatus, and per[used through the coronary arteries with an oxygenated salt solution containing glucose. The rate and amplitude of contraction were recorded mechanically on a moving paper strip, and the rate of perfusion was measured by means of a flow-meter. While the heart was beating vigorously, varying amounts of streptolysin O, previously activated with cysteine, were introduced into the perfusion fluid, and the effects on the rate and amplitude of contrac-