5 



Regulatory Mechanisms in 

 Energy Metabolism 



Jan van Eys ^ 



Introduction 



Cellular metabolism cannot be readily subdivided into neat sepa- 

 rate sections which work independently. There are, however, se- 

 quences of reactions which are generally considered as having the 

 primary function of donating chemical compounds which are re- 

 quired for anabolic processes. Thus the tricarboxylic acid cvcle, 

 while it does donate substrates for biosynthetic processes, is thought 

 of primarily as a generator of ATP.^ Similarh- the Embden-Meyer- 

 hof pathway donates ATP under anaerobic conditions and donates 

 the fuel for the tricarboxvlic acid cycle under aerobic conditions. 

 The hexose monophosphate shunt is now thought of as a donor of 

 TPNH. 



Since the need of ATP and TPNH will vary, it is only logical that 

 the rate at which these substances are supplied is variable, depend- 

 ing on the conditions of the cell. However, in spite of the really 

 staggering amount of work which has been devoted to the mecha- 



1 Department of Biochemistry, Vanderbilt University, Nashville, Tennessee. 



- Original data in this review were obtained with support of the National Science 

 Foundation Grant 5833 and United States Public Health Service Grant R.G. 7275. 



?• Investigator in the Howard Hughes Medical Institute. 



■* Abbreviations used in this paj^>er are: AMP, ADP, and ATP: adenosine mono- 

 phosphate, diphosphate, and triphosphate, respectively; DPN and DPNH: oxidized 

 and reduced diphosphopyridinc nucleotide; TPN and TPNH: oxidized and reduced 

 triphosphopjridinc nucleotide, 



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