750 VII. LIPID DISTRIBUTION IN SPECIFIC TISSUES 



cause of its tendency to form strands, on drying from aqueous solution, 

 which show good orientation under polarized light, is freely soluble in 

 water and chloroform. 266 It was reported to be present in gray matter 

 to the extent of 0.6 to 0.7% on a wet basis. Among its constituents are 

 fatty acids, sphingosine or a sphingosine-like substance, a carbohydrate, a 

 primary amine combined with the strandin molecule through its NH 2 

 group, and a chromogenic group. The minimal molecular weight as esti- 

 mated by its behavior on ultracentrifugation 266 has been placed at 250,000. 

 e. Miscellaneous Components in the Brain. There are a number of 

 water-soluble components in the brain fraction defined as extractives, 

 which are related to the lipids. The extractives from brain are similar 

 qualitatively to those from muscle and other tissues; however, from a 

 quantitative standpoint, they exhibit marked variations. 



(a) Inositol and Diphosphoinositide. The quantity of inositol is un- 

 expectedly large in brain. It constitutes 0.19% of the gray matter and 

 0.22% of the white matter. 217 Its function is unknown. A related com- 

 pound, from which inositol undoubtedly originates, is diphosphoinositide. 

 This substance, which is bound to protein by a bond which is resistant to 

 solvent action, can be extracted from a brain homogenate with a 2:1 

 chloroform-methanol mixture. 265 It appears to be a constant component 

 of brain lipids. 



(b) Ethanolamine-O-Phosphoric Acid. Ethanolamine-O-phosphoric acid 

 is a second water-soluble product, recently isolated from brain by Ansell 

 and Dawson. 267 On the basis of the proportion of this compound labeled 

 after the injection of a solution containing P 32 , it was suggested that the 

 main portion of the ethanolamine phosphate had originated by synthesis 

 rather than by a degradation of phosphatidylethanolamine. However, 

 Ansell and Dawson were unwilling to exclude this acid as a possible pre- 

 cursor for phosphatidylethanolamine. 



(c) Acetylcholine. This is the most important constituent in the water- 

 soluble extractives which is related to lipids. Since the classical experi- 

 ments of Loewi, 268 it has been recognized that this substance is set free in 

 heart muscle when the vagus nerve is stimulated. Subsequently, it was 

 demonstrated that a similar reaction occurs at the nerve endings of the 

 parasympathetic nerves when a voluntary muscle is stimulated, resulting 

 in the liberation of acetylcholine. Apparently, acetylcholine can like- 

 wise be produced in the brain on stimulation of the nerve cells, but the 



268 J. Folch, A. Arsove, and J. A. Meath, J. Biol. Chem., 191, 819-831 (1951). 



267 G. B. Ansell and R. M. C. Dawson, Biochem. J., 50, 241-246 (1951). 



268 O. Loewi, Arch. ges. Physiol. (Pfliiger's), 189, 239-242 (1921). 



