The relative level of mRNA expression was calculated by the 2-ΔΔCT method according to Real-Time PCR Application Guide (Additional file 2). Detection of phospholipase C (PLC) and perfringolysin O (PFO) PLC and PFO activities were measured according to the methods previously described [7, 30, 33]. The hemoglobin release from red blood
cells in the presence of perfringolysin buffer was measured to detect perfringolysin O (PFO) according to the method of O’Brien and Melville . The increase in turbidity of lecithin in egg yolk emulsion or the release of nitrophenol from O-(4-nitrophenyl-phosphoryl) choline as the AZD5582 mw result of hydrolysis by PLC was used to measure phospholipase C (PLC) activity [7, 30]. Collagenase assay The amounts of collagenase in the mutants and wild types were calculated by the method ON-01910 chemical structure of Awad et al.  by measuring the amount of dye released from Azo Dye Impregnated Collagen (azocoll) (Sigma). Azocoll powder was washed and resuspended in 0.2 M of borate buffer (pH 7.2) containing 0.15 M NaCl, 20 μM ZnCl2 and 5 mM CaCl2 to a final concentration of 5 mg azocoll selleck compound per ml. Next, 100 μl of the filter-sterilized supernatants of centrifuged wild types and mutants were added to 400 μl of azocoll solution and the mixtures were incubated for 2 h at 37°C. Following
centrifugation at 16,100 × g, the released dye was measured by the absorbance at 550 nm. Assay for clostripain A clostripain substrate, N-carbobenzoxy-L-arginine p-nitroanilide (Z-Arg-pNA) Anacetrapib (Bachem Americas, Torrance, CA), was used for measuring the amounts of clostripain in the supernatants of wild types and mutants . The filter-sterilized
supernatant from each centrifuged strain was incubated overnight at 4°C in a buffer containing dithiothreitol to reduce the thiol group of the cysteine residues of clostripain. Next, 20 μl of the sample was added to the 300 μl buffer containing 2 mM CaCl2 and 260 mM of Z-Arg-pNA. The kinetics software of the spectrophotometer was programmed to measure the absorbance at 410 nm every min for 30 min. The amount of cleavage of Z-Arg-pNA was measured and the enzyme units were calculated. One unit was defined as the amount of enzyme that hydrolyzed 1.0 μmol of Z-Arg-pNA per min . Detection of sialidase Sialidase activity was measured in filter-sterilized supernatants of centrifuged cultures of mutants and wild types, using 4 mM 5-bromo-4-chloro-3-indolyl-α-D-N-acetylneuraminic acid, sodium salt . The assay reaction was performed in 96-well plates by addition of the supernatant to wells containing the substrates, according to a procedure recommended by Sigma for measuring recombinant C. perfringens neuraminidase. The kinetics software was programmed to measure the absorbance at 595 nm. Hyaluronidase detection The amounts of hyaluronidase in the filter-sterilized supernatants of centfifuged wild types and mutants were quantified by measuring the degradation of hyaluronic acid.