14 METABOLISM IN THE NORMAL FUNCTIONAL STATE 



in type similar to those found with the nucleic acids from other 

 tissues (Bendich et al., 1956; Bradley and Rich, 1956). The 

 residual organic phosphorus fraction has been shown to contain 

 inositol phosphates combined with protein and lipid as phosphatido- 

 peptides (LeBaron and Folch, 1956), and also a phosphorus 

 containing fraction from which inositol was absent (Vladimirov 

 et al., 1957) and which was not a phosphoprotein. Middleton 

 (1953) is reported to have shown that the Schmidt-Thannhauser 

 digest of the residual organic phosphorus contains some seven 

 different fractions at least two of which contain inositol. These 

 examinations of the nature of the phosphorus in the residual 

 fraction are the beginnings only of a study that is likely to prove 

 difficult and prolonged, for the fractions which have so far been 

 obtained have necessitated extensive degradation of the original 

 material. 



Similar obscurity exists regarding the phosphoprotein fraction. 

 This has been shown to yield phosphoryl serine on acid hydrolysis 

 (Heald, 1958; Vladimirov and Pravdina, 1956), a property in 

 common with many phosphorylated proteins. It has been sug- 

 gested (Englehardt and Lissovskaya, 1953; Rossiter, 1955) that 

 the phosphorus is that of enzyme substrate complexes. It seems 

 unlikely that the major part of the phosphorus arises from such 

 sources. The enzymes known to be phosphoproteins and to yield 

 phosphoryl serine on acid hydrolysis are yeast hexokinase (Agren 

 and Engstrom, 1956), liver phosphorylase (Wosilait, 1958) and 

 pepsin (see Neurath, 1957) with the possible inclusion of yeast 

 phosphoglucomutase (Sidbury and Najjar, 1953). Excluding 

 pepsin, which is absent, the rates of the reactions catalysed by the 

 equivalent enzymes in brain are known (Mcllwain, 1959). Assum- 

 ing the brain enzymes to contain similar quantities of phosphorus 

 it can be calculated from data already available (Colowick and 

 Kaplan, 1955) that they contribute not more than 1-2% to the 

 phosphorus of the phosphoprotein fraction. Present evidence 

 (Heald, 1959) indicates that the phosphoproteins of brain con- 

 stitute two main fractions, the larger of which appears to be a 

 single entity as regards phosphorus exchange. This phospho- 

 protein fraction is metabolically extremely active and discussion of 

 its metabolic role in brain is given later (pp. 120-22). 



In contrast to the phosphates soluble in acid denaturants it can 

 be seen that those remaining constitute by far the greater quantity 



