FORMATION OF PHOSPHATIDES IN THE BRAIX TISSUE OF ADILT ANIMALS 25!^ 



the labelled lecithin was already formed after the lapse of a few minutes, 



, . , . , ,. mass of inorganic P . , , , , , 



at which time the ratio in the blood was smaller 



activity 



and 1 activity unit therefore indicated a smaller mass of phosphorus 



than after the lapse of one hour when the measurements were actually 



made. Hence the actual amount of labelled lecithin phosphorus will 



be less than that calculated above but is definitely higher than 0.08 mgm. 



PHOSPHORUS EXCHANGE IN BRAIN LECITHIN IN VITRO 



We shook a freshly removed rat brain for 5 hours at 37° with 3 cc. 

 ol' an isotonic sodium chloride solution containing 0.09 mgm of phos- 

 phorus labelled by the addition of radioactive phosphorus. The brain 

 was carefully washed with cold acetone and dried at room tempera- 

 ture and the lecithin extracted as described above. The ethereal solu- 

 tion was shaken for several hours with sodium phosphate to remove 

 inorganic labelled phosphorus and after this operation had been repeat- 

 ed four times, the sodium phosphate was found to be entirely inac- 

 tive. The solution showed an activity of 2200 units and we found 18 

 units in the lecithin extract; this corresponds to 0.00076 mgm of label- 

 led phosphorus or about ^I^qqq part of the total lecithin phosphorus 

 content of the brain. Thus the formation of a very small amount of 

 labelled phosphorus also takes place in the freshly removed brain tissue 

 in vitro, presumably under enzymatic action. We intend to follow up 

 the exchange problem ii} vitro in greater detail. 



DISCUSSION OF THE RESULTS 



From the results above it clearly follows that brain lecithin is con- 

 stantly being synthesized in the brain tissue of adult animals. Pre- 

 sumably a part of the lecithin is constantly broken down under enzy- 

 matic action and rebuilt again, thus making it possible for the labelled 

 phosphorus atoms present in the blood to enter the lecithin molecule. 



Belfanti, Contardi and Ercoli (1936) give the following scheme 

 according to which lecithin is supposed to decompose under the action 

 of lecithases. 



It is possible that a reaction takes place in both directions according 

 to this or a similar scheme, so that the phosphorus atoms present in 

 lecithin, are rendered exchangeable when enzymes are present although 

 they undergo no exchange in the absence of these. The study of the 

 mode and rate of action of the different lecithases may be much facili- 

 tated by following up exchange process in lecithin and its decomposition 

 ])roducts in 1ho prosonoo and absence of the flifferent enzvmes. 



