Streptolysin O II. Relationship of Sulfyhdryl Groups to Activity

Abstract

Streptolysin O (SO), a group A streptococcal toxin, exists in two forms, a reduced active state and an oxidized reversibly inactive state. Activity is measured by red blood cell hemolysis. SO is a labile toxin, and, with time, activity is irreversibly lost. The rate of activity loss is slowed by incubation with 0.1 m 2-mercaptoethanol or 0.01 m ethylenediaminetetraacetic acid (EDTA). The effect of EDTA can be reversed by excess MgSO 4 . Reversibly oxidized SO is activated by cleavage of disulfide bonds. When the free sulfhydryl groups of the active SO are alkylated with iodoacetamide, complete and irreversible loss of activity results. Periodate (0.01 m ) oxidation also causes complete loss of activity which may be due to oxidation of sulfhydryl groups. SO in the active form reacts with Fe 2+ , Cu 2+ , Ca 2+ , and Mg 2+ , causing loss of activity in various degrees depending on the ions and the concentration used. Ferric and cupric ions are most effective and cause loss of activity at concentrations on the order of 10 −4 m . The reversibly oxidized form of SO is not influenced by exposure to cupric ions (0.01 m ), indicating that the reaction is only with the active form of SO, probably involving the free sulfhydryl groups. These groups may be responsible for the direct binding of the toxin to the target membrane or for the maintenance of the proper conformation for activity.

Characteristics of Streptolysin O Action

“…Although SO must be in its reduced form for adsorption to occur, the possibility that disulfide bridges between the toxin molecule and an erythrocyte membrane protein are involved seems unlikely; cells treated with sulfhydryl inhibitors remained susceptible to toxin. A similar observation was reported by van Epps and Andersen (16), who showed that alkylation of membrane sulfhydryl groups with iodoacetamide did not prevent SO hemolysis. In addition, the finding that cells treated with various proteolytic enzymes were lysed by SO argues against a role for external membrane proteins in the adsorption process.…”

Pathogenicity Induced by Invasive Infection of Streptococcus dysgalactiae subsp. equisimilis in a Mouse Model of Diabetes

“…Incubation of a 5% suspension of sheep red blood cells with SDSE-167 for 3 h resulted in significantly greater hemolysis compared with strains SDSE-168, SDSE-117, M1 GAS-476, and M1 GAS-SMD ( Figure 1A ). SLO is inactive in the absence of a reducing agent such as 2-mercaptoethanol ( Van Epps and Andersen, 1971 ). SLS is oxygen-stable but its activity is inhibited by trypan blue ( Taketo and Taketo, 1982 ).…”

Interaction of streptolysin O from Streptococcus pyogenes and theta-toxin from Clostridium perfringens with human fibroblasts

“…Our results are in agreement with the latter investigation and show that theta-toxin also interacted similarly with these cations (Table 1). The inhibiting effects of Zn2à nd Ca2`may be due to a direct inhibitory action on the toxins, e.g., by reaction with free SH groups (5,37). These ions are also known to have a stabilizing effect on the fibroblast plasma membrane (24, 39), which may render it less susceptible to any membrane-damaging activity.…”