ENZYME-SUBSTRATE COMPOUNDS AND 

 ELECTRON TRANSFER* 



BRITTON CHANCE, Johnson Research Foundation, University of 

 Pennsylvania, Philadelphia, Pennsylvania 



The search for intermediates in enzyme reactions began 

 with the hyperbolic relationship between the over-all reaction 

 rate and the substrate concentration: Henri (39), Brown (2), 

 and Michaelis and Menten (52) formulated a mechanism for 

 enzyme action involving a single intermediate compound. 

 Direct experimental studies have identified such intermediate 

 compounds in iron porphyrin and pyridine nucleotide enzyme 

 systems (4,18,43,60,66-68) and experiments on their reaction 

 kinetics have shown them to participate directly in the enzymatic 

 sequence. But other compounds formed in the enzyme- 

 substrate reaction have been found to be definitely inhibitory 

 (5,6) or to have no function (6,32,42,43). Analogous com- 

 plexities arise in sequences of enzyme reactions, for example, 

 cytochrome b has been identified as a nonfunctional component 

 of the nonphosphorylating DPNH (63) and succinate (12) 

 oxidase system of heart muscle particles, whereas it participates 

 actively in the phosphorylating system. From such a confusing 

 array of reactive and unreactive intermediates we must identify 



* Much of the work of this laboratory referred to in this contribution was 

 supported in part by the United States Public Health Service, the National 

 Science Foundation, and the Office of Naval Research. 



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