Biosynthesis of Cyclopropane Compounds

Several natural and synthetic phospholipids can serve as substrates for the cyclopropane synthetase enzyme of Closfridium bufyricum. The conditions for optimum substrate effectiveness vary with the substrate; e.g. an anionic surfaceactive agent is necessary with phosphatidylethanolamine, while divalent cations stimulate the rate of reaction with anionic phospholipids. These variable conditions probably provide the optimal surface charge on the phospholipid aggregates for most efficient enzyme-substrate interaction. A diether analogue of phosphatidylethanolamine, l,Z-di(Q-octadecenyloxy)-3-(2-aminoethyl)phosphorylpropane, is an effective substrate for cyclopropane synthetase, indicating that the ester carbonyl groups are not essential for activity. When presented with a racemic mixture of dioleyl phosphatidylethanolamines, the enzyme acts nearly exclusively upon the 3-phosphoglycerol isomer. Cyclopropane synthetase acts upon phospholipids deposited upon Nter paper discs. The pattern of activity with various phospholipids is difFerent from that with the compounds dispersed in buffer, and no accessory substances such as surface-active agents or divalent cations stimulate the reaction on filter paper.