ENZYME-SUBSTRATE COMPOUNDS 



these voltages are carried out in accordance with equations 

 similar to (16) and (17) above. The concentrations of the 

 reactants are multiplied together in an electronic multiplier, 

 the product is multiplied by the fixed value of the reaction 

 velocity constant, the terms corresponding to a particular 

 reaction rate are summed with an "adder," and the sum is 

 integrated with respect to time in an electronic integrator. The 

 concentration of one of the reactants determined in this way is 

 automatically substituted into the appropriate place in the 

 differential equations. A similar process gives the values of 

 concentration of all the other reactants which are substituted 

 into the appropriate places in the equations. The solution then 

 continues, just as does the chemical reaction, until one of the 

 reactants is used up. In equations (13), (14), and (15) we 

 would choose oxygen to be limiting in concentration so that the 

 reaction would halt with the components in the reduced form. 

 The reaction is then readily restarted by adding a voltage pro- 

 portional to the desired initial oxygen concentration. For 

 convenience the computer solution is restarted every 0.1 sec. 

 so that a continuous pattern of solutions is displayed on the 

 screen of a cathode-ray tube. A typical series of traces for a 

 sequence of four catalytic reactions is illustrated by Fig. 5A. 



The solution of these equations for short times is shown by 

 Figure 5B. In this case it is easy to see that the time sequence is 

 the same as the chemical sequence. It should also be noted 

 that there is a perceptible delay in the oxidation of the com- 

 ponents farther from oxygen; one component must achieve a 

 considerable oxidation before the next one in the sequence is 

 oxidized perceptibly.* 



REGENERATIVE-FLOW METHOD 



In the study of pure soluble enzymes the chief obstacle has 

 been the supply of material, and for this reason the stopped- 

 flow method has been evolved, which requires only 10~^° mole 

 of reactants for very rapid reactions. The turbidity of whole 



* The studies were largely carried out by Mr. J. Higgins and Mr. W. 

 Holmes. 



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