80 METABOLIC PATHWAYS IN MICROORGANISMS 



This has been verified quantitatively (24). When the gravi- 

 tational field is increased to 144,000g, all the pentose cycle 

 enzymes are precipitated together (not shown); for this 

 reason we are often tempted to refer to the pentose cycle as 

 a complex; and although it may not be safe to draw firm 

 conclusions on such indirect evidence, nonetheless we are 

 taking as a working hypothesis the view that the entire com- 

 plex may be an intact submicroscopic unit within the cell. 

 These two major dissimilation pathways thus appear to 

 exist side by side in different parts of the cell. An inter- 

 esting point would be the determination of the control 

 agents that may be operating in vivo to direct the sub- 

 strate into one or the other pathway. This is as yet un- 



TABLE 3.4 



Effect of Pyridine Nucleotides on Specific Activity of C^^Oo 

 Arising from Labeled Glucose in Pig Heart Homogenates 



CiVCe' * 



No Pyridine 

 Size Nucleotides DPN TPN 



Adult 1.00 1.02 2.29 



Fetal (5.5 in.) 1.09 1.47 14.24 



Flask components: 460 /zmoles of KCI; 20 //moles of phosphate 

 buffer, pH 7.4; 200 /xmoles of nicotinamide; 10 //moles of MgClo; 

 0.14 /imole of cytochrome c; 10 //moles of ATP (K salt); 10 /imoles 

 of glucose, 3 //moles of pyridine nucleotide; 2 ml. of homogenate in 

 tris buffer; 0.3 //c. of labeled glucose. The volume was 4.15 ml.; 

 the temperature, 37°; and the time, 5 hours. 



* d' specific activity of C'^O? from glucose- l-C^"* 

 Ce' specific activity of C^'*02 from glucose-6-C^^ 

 After Jolley, Cheldelin, and Newburgh (29). 



