Special Section on Bacterial Phospholipases C as Exotoxins

More than 60 years ago, studies on bacterial phospholipases C started with the monumental work of Macfarlane and Knight (1941). According to their study, Clostridium perfringens a-toxin having lethal, necrotic, and hemolytic activities, proved to be an enzyme ‘‘lecithinase’’ that hydrolyzes lecithin, i.e., phosphatidylcholine, into diacylglycerol and phosphorylcholine. From various points of view, this discovery was epoch-making. First, it indicates that a single enzyme can be a major lethal toxin of C. perfringens. Afterward, several other toxins, such as diphtheria toxin, proved to be enzymes. Therefore, C. perfringens a-toxin is the first bacterial toxin recognized as an enzyme. Second, this discovery poses an inevitable question. How does this enzyme exert its toxic action against host cells, leading to the