THK PHOSPHATIDIC ACIDS 469 



separation of the ether-insoluble and ether-soluble lead salts, the iodine 

 numbers of the respective fractions were 44 and 173. 



{5) Enzymic Breakdown of Phosphatides to Phosphatidic Acids 



That the phosphatidic acids may not be primary products in nature but 

 may rather be intermediates in the breakdown of lecithin, phosphatidyl- 

 othanolamine, or phosphatidylserine, seems possible in view of the recent 

 demonstration of an enzyme present in plants which is capable of splitting 

 off the nitrogenous base from these compounds. Phosphatidic acid would 

 be the residue which remains. This enzyme was first demonstrated by 

 Hanahan and Chaikoff^'^^ in raw carrot. It was later shown^''^ to have an 

 optimum pH between 5.2 and 5.9. The enzyme exhibits a high degree of 

 stability toward heat; it is not completely inactivated when exposed to a 

 temperature of 95°C. for 15 minutes. 



The same enzyme has recently been shown to be present in cabbage 

 leaves."'' Hanahan and Chaikoff"" believe that, in the preparation of 

 phosphatidic acid, the enzyme set free by maceration of the leaves hy- 

 drolyzes the phospholipid to phosphatidic acid. These investigators were 

 able to prepare phosphatidic acid when they followed the procedure of 

 Chibnall and Channon.^*^-^ However, when the enzyme was largely 

 destroyed by steam treatment prior to maceration and extraction, a phos- 

 pholipid high in choline and nitrogen was isolated from cabbage leaves, in 

 place of phosphatidic acid. One must assume, therefore, that phosphatidic 

 acid probably does not exist as a primary product; however, since it so 

 readily originates by enzymic breakdown of the phospholipids, it must be 

 considered to be of importance as an intermediate. 



(6) Compounds Related to Phosphatidic Acid 



Cardiolipin is a phospholipid present in beef heart which is now believed 

 to be a phosphatidic acid. Pangborn"^ coined the name for a substance 

 prepared from beef heart which is responsible for the reaction with the sera 

 of syphilitics. Since the work of Noguchi,'^"- it has been recognized that 

 the antigenic action of beef heart preparations is associated with an ace- 

 tone-insoluble fraction, but it has been uncertain which phosphatide is in- 

 volved. Although impure lecithin preparations have been described as 



'«8 D. J. Hanahan and T. L. Chaikoff, /. Biol. Chem., 168, 233-240 (1947). 

 '«» D. J. Hanahan and I. L. Chaikoff, J. Biol. Chem., 169, 699-705 (1947). 

 '™ D. J. Hanahan and I. L. Chaikoff, J. Biol. Chem., 172, 191-198 (1948). 

 3'i M. C. Pangborn, ./. Biol. Chem., 143, 247-256 (1942). 

 "2 H. Noguchi, Z. Immunitdts., 9, 715-749 (1911). 



