42 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



substrate. Otherwise, a velocity constant further along the reaction se- 

 quence may be measured (16). 



In addition to the advantage that a rapid flow apparatus is not needed, 

 this equation has the advantage that neither substrate nor hydrogen donor 

 concentrations need be known and in cases where e is measured inde- 

 pendently, for example, by an activity assay or by physical methods, the 

 experiment need only give the fractional amount of enzyme in the form 

 of enzyme substrate and compound and the half-life of the intermediate. 

 Both these quantities can be measured rather accurately. 



Fig. 3. Illustrating the quan- 

 tities measured from the kinet- 

 ics of the enzyme substrate com- 

 pounds in order to compute the 

 velocity constant for the forma- 

 tion of the intermediate. The 

 diagram is a differential ana- 

 lyzer solution for the kinetics of 

 appearance and disappearance 

 of the enzyme substrate com- 

 pound of equations 1 and 2 for 

 the conditions 1 ixm substrate. 

 The units of the abscissa are 

 seconds for ki is ecjual to 10" 

 M"^ sec"\ The value of Ks 

 (= k4a of equations 2 and 3) is 

 0.5 sec~^ and ko of equation 1 is 

 0. The figure illustrates the 

 measurement of the quantities 

 e — p^ and U^^ff of equation 5. 

 For more details see ref. 16. 

 Data from Arch. Biochem. 



0.5 



This equation has been applied to the determination of the reaction 

 velocity constant for the formation of the intermediate compound in per- 

 oxidase action and the effect of temperature upon this velocity constant. 

 These data are illustrated in figure 4 and it is seen that a heat of 3600 cal. 

 is obtained. The room temperature value for the velocity constant is in 

 close agreement with that obtained directly by the rapid flow method. In 

 cases where the substrate (xo) and hydrogen donor concentrations (ao) 

 are known, the following equation may be used to calculate k^ , the velocity 

 constant for the reaction of the enzyme-substrate compound and hydrogen 

 donor: 



k4 = Xo/ao Pmtioff (6) 



and figure 4 includes the effect of temperature upon this velocity constant. 



