92 CYTOCHEMISTRY OF ALDEHYDES 



The Significance of Aldehyde Acetal 



Feulgen and his colleagues showed that, whereas some free al- 

 dehyde (which they originally called plasmal) exists in tissues, a 

 large part of the naturally occurring aldehyde occurs as the 

 acetal phosphate of glycerol (which they called plasmalogen), as 

 shown in Formula III. The acetal phosphate III has been shown 

 to be a common constituent of tissues. Its mode of formation is 

 not at present clear. If an aldehyde phosphate occurs in tissues, 

 it might well combine spontaneously with glycerol as indicated 

 in I, to give the compound II. This latter compound would prob- 

 ably pass spontaneously into III by wandering of the phosphate 

 radical, as occurs in the equilibrium between a- and ^-glycero- 

 phosphates. Alternatively, it may be that the compound III is 

 derived by condensation of free aldehyde and glycerophosphate 

 to give the acetal phosphate. Various hypotheses could be put 

 forward for the function of the acetal compound III. It might 

 be concerned in fatty-acid metabolism, in the formation of tri- 

 glycerides or in the formation of phospholipins. But there is 

 little evidence available on these points as yet. 



R R 



I I 



CH CH 



/ \ / \ 



OH OPO3H2 O OP0 3 H 2 



+ 

 HO OH 



OH 

 CH 2 — CH— CH 2 OH 2 



CH 2 — CH— CH 2 OH 



1 11 



R 



CH 

 / \ 



o 



CH 2 CH— CH 2 OP0 3 H 2 



in 



The Study of Glycols in Tissues 



Groups such as — CHOH— CHOH— do not react directly with 

 any of the reagents for aldehydes. Recently, however, it has been 

 shown that periodate reacts in a fairly specific manner with these 



