Convenient biosynthetic preparation of isomeric spin-labelled radioactive phosphatidic acids

A convenient method for the enzymatic preparation of sn-3-[2-3H]phosphatidic acids carrying also 5-, 12-, or 16-nitroxide stearic acids, from sn-3-[2-3H]glycerophosphate and isolated guinea pig liver microsomes, is described in detail. The procedure allows a simultaneous preparation of three spin-labelled sn-3-[2-3H]phosphatidic acids of yields 3-3.5 mumol of each compound which is greater than 99% pure in respect to the radioactivity and which contains 25 mol% of spin-labelled fatty acids. These phosphatidic acids were approximately equally distributed between the primary and the secondary hydroxyl when 12- or 16-nitroxide stearic acids were used or predominantly (75%) associated with the secondary hydroxyl of sn-3-[2-3H]phosphatidic acid when 5-nitroxide stearic acid was present in the incubation mixture.