PARATHYROID HORMONE AND RAT ( ALVARIA METABOLISM 



599 



Substrate Utilization 



The Qo.2 remains stable for manv hours with no added substrate. 

 From this, it is obvious that an adequate supplv of the intermediates 

 and substrates exists for the system or systems responsible for oxygen 

 uptake. At no time during this period will addition of TCA cycle 

 intermediates (with the exception of succinate as discussed above) 

 alter the Qo.^. If oxygen uptake is taking place in the TCA cycle, it 

 follows that a continuous supplv of dicarboxvlic acids is available, 

 either through CO2 fixation or by transamination reactions involving 

 alpha ketoglutarate. The intracellular store of carbohvdrate which is 

 being oxidized must be of considerable size. Glycogen is histolog- 

 ically demonstrable in the tissue and, chemically, is present in ade- 

 quate amount to maintain the observed Qo.^ for over 8 hours. The 

 content is some 4.5 mg per gm wet weight, equivalent to 25 moles 

 of glucose and requiring 150 moles of oxygen for complete oxidation. 

 Based on a ()(.o of 18.4 moles/gm wet wt/hr., it would therefore be 

 adequate for just over 8 hours if the lactate initially formed were 

 later metabolized. 



The glycogen content was determined before and after a 2-hour 

 incubation and the results are given in Table V, expressed as the 

 quantitv of glvcogen hvdrolyzed, i.e. no longer precipitable with 

 alcohol, with its calculated glucose equivalent. By expressing the 

 lactic acid production and the Qo.j in the same manner, a striking 



TA15LK y. IvxDOGKNOus and I'>xogenou.s Substrate I'tilization 

 (Phospliatc medium; 100 i)('r cent Oj; mean values of 6 to 12 flasks) 



" Mg/gm wet weight. 

 '' Glucose, 30 mg %. 



