Streptolysins O and S from hemolytic streptococci have been added to granular fractions of tissue homogenates in 0.25 M sucrose prepared from rabbit liver, heart, spleen and lymph nodes. At concentrations ranging from 0.65 µg/ml to 2.0 mg/ml of streptolysin S, and from 10 µg/ml to 1.0 mg/ml of streptolysin O, two lysosomal enzymes (beta glucuronidase and acid phosphatase) and, to a lesser degree, one mitochondrial enzyme (malic dehydrogenase) were released into the supernatants of the reaction mixture. Although the hemolytic action of each lysin paralleled the effect on lysosomes, at equivalent levels of hemolytic activity, SLS was approximately 10 times more active on lysosomes than SLO. SLO was inhibited by cholesterol, cortisol, and specific antibody in vitro; pretreatment of animals with cortisone decreased the susceptibility of their isolated lysosomes to SLO. These agents failed to prevent SLS action on lysosomes. SLO had a pH optimum of 6.5 against lysosomes while SLS was maximally active at 7.5. No other streptococcal extracellular products were as active on lysosomes as the streptolysins, although activated streptococcal proteinase precursor released some hydrolases from the granules. Similarities between the actions of SLO and SLS on red cells and lysosomes suggested that the membranes bounding lysosomes and erythrocytes have common properties.

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