FACTORS AFFECTING METABOLISM in vitro 



117 



adenosine triphosphate (Table 18), while at the same time the 

 specific radioactivity of the tissue residue increased. Thus an 

 increased exchange of radioactive phosphate had taken place 

 between the highly labelled acid-soluble phosphates and some less 

 highly labelled unknown tissue component. 



240 



200 



160 



Fig. 13. The time course of incorporation of radioactive phos- 

 phate into guinea pig cerebral slices incubated in salines con- 

 taining glucose. Tissues were removed at the time indicated by 

 the arrows A, washed for 10 sec in saline and reincubated in 

 fresh saline. + = orthophosphate ; # = adenosine triphos- 

 phate y-P; O = phosphocreatine ; A = hexose monophosphates. 

 The relative specific radioactivity is the specific radioactivity of 

 a phosphate (counts/min per ^^gP) relative to a standard specific 

 radioactivity of the inorganic phosphate in the medium. Data 

 from Heald (19566). 



Analysis of the acid-insoluble tissue residue after incubation 

 of slices with radioactive phosphate followed by the passage of 

 electrical pulses for 10 sec, showed that only the phosphorus of the 

 phosphoprotein fraction increased in radioactivity (Heald, 1957^), 

 the changes in the nucleic acids, residual organic phosphorus and 

 the phospholipids being insignificant. The quantities of phospho- 

 protein did not change as a resuh of the stimulus the levels remain- 

 ing constant at M6-M7 jitmoles phosphorus/g wet wt. Thus, the 



