Bacterial hemolysins are exotoxins that attack blood cell membranes and cause cell rupture. Constitutes an essential virulence factor in gas gangrene. Binds to eukaryotic membranes where it hydrolyzes both phosphatidylcholine and sphingomyelin. The diacylglycerol produced can activate both the arachidonic acid pathway, leading to modulation of the inflammatory response cascade and thrombosis, and protein kinase C, leading to activation of eukaryotic phospholipases and further membrane damage. Acts on human and mouse erythrocytes, but not on rabbit or horse erythrocytes. a 1,2-diacyl-sn-glycero-3-phosphocholine + H2O = a 1,2-diacyl-sn-glycerol + H(+) + phosphocholine Binds 3 Ca(2+) ions per subunit. Binds 3 Zn(2+) ions per subunit. The protein is composed of 2 domains; the N-terminal domain contains the phospholipase C active site (PLC), in a cleft which is also occupied by the 3 zinc ions. The C-terminal domain is a putative phospholipid-recognition domain, which shows structural homology with phospholipid-binding C2-like domains from a range of eukaryotic proteins. The ability to bind membrane phospholipids in a Ca(2+) dependent manner and toxicity is conferred by this C-terminal domain, which also contributes to the sphingomyelinase activity. Vaccination of mice with a fragment (residues 275-398) protects them against a subsequent challenge with purified alpha-toxin. Two main forms of alpha-toxin can be purified from C.perfringens; a major form with a pI of 5.48, and a minor form with a pI of 5.6. Both are equally active. Variations seen in PLC activity between different strains may be due to transcriptional regulation. Mutating residues 303 or 359 of the C.perfringens toxin to match those found in C.bifermentans (301 and 358 respectively) reduces toxicity considerably. Belongs to the bacterial zinc-metallophospholipase C family.