The distribution of fatty acids in purified phospholipids isolated from several different bacteria has been examined by use of the specific phospholipase A of snake venom. In general the distribution is in accord with that found elsewhere in nature; the unsaturated acids are found in the β position and the saturated acids in the γ position. The distribution of cyclopropane fatty acids follows closely that of the unsaturated fatty acids. A notable exception was encountered with the phosphatidylethanolamine of Clostridium butyricum, in which unsaturated and cyclopropane fatty acids were found in more abundance in the γ position. The specificity of the C. butyricum cyclopropane synthetase reaction has been examined by employing as substrate a phosphatidylethanolamine with a known distribution of unsaturated fatty acids and analyzing the distribution of cyclopropane fatty acids in the phospholipid produced by the enzyme reaction. These experiments indicate that the enzyme has a definite, but not absolute, specificity for an unsaturated fatty acid in the γ position.
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