432 V. CHEMISTRY OF PHOSPHATIDES AND CEREBROSIDES 



cifically supplied. Since the growth of this fungus is proportional to the 

 amount of choline present when a suboptimal range of choline is available, 

 the weight of Neurospora produced under certain standardized conditions 

 may be used as a method for the quantitative measurement of choline. 

 With the so-called choUneless strain, crude extracts can be analyzed, as the 

 substances which interfere with the periodate or reineckate methods are 

 entirely inactive. Combined choline is not determined unless hydrolysis 

 has been carried out previously. This method has the advantage not only 

 of being specific but also of possessing a very high sensitivity. However, it 

 does require several days for the completion of a test. A description of 

 methods for carrying out this procedure is given by Horowitz and Beadle,^" 

 as well as by Luecke and Pearson. ^^" 



c. Glycerophosphoric Acid. Glycerophosphoric acid is one of the end 

 products of the hydrolysis of lecithin, especially when alkali is employed. 

 The hydrolysis of the linkage between glycerol and phosphoric acid appears 

 to be difficult, and the organic phosphate is the usual end product. Levene 

 and Rolf^^* first identified glycerophosphate as a hydrolysis product of 

 "cephalin," which they believed to be identical with the product obtained 

 from lecithin. Glycerophosphates have also been prepared from plant 

 phosphatides.34'«^'i4i-i^=*'i^^'i8^-i9« 



Two types of glycerophosphates are known, depending upon whether the 

 phosphoric acid is combined with the glycerol through the hydroxyl group 

 on the a- or on the /^-carbon atom. These have the structures shown here. 



HjCOH H2COH -„ 



H^OH ^oH HC-0-P=0 



H2C-0-P=0 H2C0H OH 



a-Glycerophos- /3-Glycerophos- 



phoric acid phoric acid 



Both types of glycerophosphates can be separated from natural sources. 

 They can be readily distinguished, since the a-form contains an asymmetric 

 carbon atom and hence is optically active, while the /3-compound is optic- 

 ally inactive. Willstatter and Ltidecke^^ concluded in 1904 that lecithins 

 have the a-structure, since optically-active ^-glycerophosphate can be pre- 

 pared from them. Although other workers were able to prepare optically 

 active glycerophosphate from other phosphatides, it was later shown that 



i»2 R. W. Luecke and P. B. Pearson, .7. Biol. Chem., 155, 507-512 (1944). 



"3 P. A. Levene and I. P. Rolf, J. Biol. Chem., 40, 1-16 (1919). 



1" V. Njegovan, Z. phi/siol Chem., 76, 1-26 (1911-1912). 



1^6 E. Schulze and A. Likieinik, Z. phtjsiol. Chem., 15, 405-414 (1891). 



196 G. Trier, Z. phijsiol. Chem., S6, 1-32 (1913), 



