96 GENERAL METABOLISM in vitro 



largely through studies of the effects of electrical stimulation upon 

 cerebral tissues and will be presented in Chapter 4. 



Nucleic Acids 



It has been unequivocally demonstrated (Deluca et al., 1953) 

 that nucleic acids in vitro are continuously synthesized and 

 degraded. In these experiments nucleic acids were extracted by 

 the method of Hammarsten (1947, see appendix) and hydrolysed 

 to nucleotides which were then separated chromatographically 

 from other radioactive contaminants before estimation. As ifi vivo 

 it was found that slices metabolizing glucose incorporated radio- 

 active phosphate almost exclusively into the ribose nucleic acids, 

 little or no radioactivity being found in the desoxyribonucleic 

 acids. The incorporation of radioactivity was the result of a true 

 metabolic exchange since no net synthesis of nucleic acids took 

 place during incubation. Nevertheless exchange was slow (Table 

 14) and compared with that of other body tissues was very slow 

 indeed. Incorporation was abolished under anaerobic conditions 

 (Deluca et al, 1953; Findlay et aL, 1953; Strickland, 1954). 



Residual Organic Phosphorus 



Experiments in vitro have so far done little to clarify the nature 

 of this fraction or details of its phosphorus metabolism. Compared 

 witli other phosphates insoluble in trichloracetic acid it incorporates 

 radioactive phosphate less rapidly than phosphoprotein but at a 

 markedly greater rate than ribonucleic acid or the total lipid 

 phosphorus (Findlay et aL, 1954). As with other fractions a 

 prerequisite for incorporation is the maintenance of aerobic 

 conditions. 



The importance of adequate oxygenation in supporting the 

 incorporation of radioactive phosphate is intimately connected 

 with the maintenance of adequate levels of energy-rich phosphates 

 in the tissue by oxidative phosphorylation. Factors altering these 

 levels or the metabolism of the energy-rich phosphates also alter 

 the metabolism of the other phosphates. Many of these factors, 

 as they relate to different substrates and inhibitors, will be con- 

 sidered in the next chapter. 



