104 



FACTORS AFFECTING METABOLISM in Vltro 



in the presence of glucose, followed by metabolism in oxygen, 

 failed to restore levels of phosphocreatine though the oxygen 

 uptake of the tissue was only slightly less than normal (Thomas, 

 1956). 



The results described in Table 16 are paralleled to a large degree 

 by the ability of the individual substrates to support the incorpora- 

 tion of radioactive phosphate into phosphorus compounds present 

 in the acid-insoluble residues of the tissue (Table 17). Thus, 

 succinate, malate, glutamate and a-oxoglutarate failed to support 

 the incorporation of phosphorus into the phospholipid, nucleic 

 acid, phosphoprotein and residual phosphorus of cat cerebral 

 slices. In many instances the degree of incorporation was less than 

 in cerebral slices metabolizing in the absence of substrate. 

 Pyruvate and lactate supported some incorporation but generally 

 to a less degree than glucose. The similarities between conditions 

 supporting exchange of radioactive phosphate with the fractions 



Table 17. — The Effect of Different Substrates upon 

 THE Incorporation of Radioactive Phosphorus into 

 the Acid-insoluble Phosphates of Cerebral Slices 



Data from Findlay et al. (1953); Findlay et al. (1954); and Strickland 

 (1954). All substrates were at final concentrations of 10 mM with the 

 exception of succinate which was 50 mM. Specific radioactivity= counts/ 

 min per fxg P. 



