Changes in the phospholipids of the membrane of L-forms of Streptococcus faecalis were studied after exposure to normal human serum. The phospholipids were labeled by incubating the L forms with [14C]palmitate. After the reaction of the L-forms with normal human serum, the percentage of total lipid radioactivity decreased in phospholipids and increased in free fatty acids, indicating phospholipase activity. Similar changes were seen on reacting normal human serum with autoclaved L-forms. Sonication of the L-forms resulted in only a slight increase in phospholipase activity. These results suggested that a major part of the phospholipase activity was in the serum.
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