FACTORS AFFECTING METABOLISM in Vttro 109 



ling. Under aerobic conditions, 2 :4-dinitrophenol decreased the 

 incorporation of phosphate into adenosine triphosphate and lowered 

 the total quantities present in addition to decreasing the labelling 

 in the phospholipids, but was ineffective anaerobically. Analysis of 

 metabolism in these systems by means of inhibitors provides a 

 method of recognizing the various enzymic stages necessary, for 

 example, to the incorporation of phosphate into a particular 

 component. The results of such an analysis show that the normal 

 phosphate metabolism of cerebral tissues requires both the 

 uninhibited functioning of all stages in the metabolism of glucose 

 and the maintenance of adequate levels of phosphocreatine and 

 adenosine triphosphate. 



Inorganic Phosphate and Phosphate Acceptors 



In vivo a variety of conditions (Chapter 2) increase the levels 

 both of inorganic phosphate and of phosphate acceptors such as 

 adenosine diphosphate and creatine. Study of the effects on 

 metabolism of different concentrations of these compounds has 

 revealed that the rate of oxygen uptake is related to the quantities 

 present in an interesting manner. 



With dispersions of pigeon brain made in 0-9% KCl and 

 dialysed against 0-4% KCl (treatment which probably preserved 

 the mitochondria) Banga et al. (1939) found that the oxidation of 

 pyruvate proceeded only slowly in the presence of inorganic 

 phosphate at 0-01 M but was greatly increased when adenylic 

 acid at 1-4 X 10~^ M was added. Similar results were obtained by 

 Long (1943, 1945) using a similar preparation; the oxidation of 

 pyruvate, a-oxobutyrate and fumarate being dependent upon the 

 presence of inorganic phosphate and the nucleotide. Adenine 

 nucleotide was required in catalytic amounts only, whereas 

 oxygen uptake showed a marked dependence upon the concentra- 

 tion of inorganic phosphate. Thus, for the oxidation of pyruvate, 

 the optimal phosphate concentfation was 0-05 M with a half 

 maximal velocity between 0-0 1-0- 05 M. At high concentrations 

 inorganic phosphate was inhibitory. 



Attention has been drawn (Mcllwain, 19526, 1959) to simi- 

 larities in the concentrations of inorganic phosphate at which the 

 most rapid increases in oxygen uptake occurred in the above 

 experiments and the concentrations existing in cerebral tissues 

 in vivo in certain physiological states. Thus concentrations of 



