34 INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



.2 .4 .6 .8 1.0 \2 1.4 IB 1.8 2.0 2.2 x 10 



Fig. 7. Variation of ki and k,i with D. 



which is far in excess of ki and k4 . The approximate surface area of this 

 molecule = 2.5 X 10^ A-. Thus the encounter rate per A- is about 2.5 X 

 10^ liters/mole • sec which is far smaller than even ki . Thus the reaction 

 cross-section, including four hemes, must be of the order of 50-100 A-. The 

 differences in k4 could be interpreted as a variation in the reaction cross- 

 section. The fact that these numbers are bigger than 4 A- indicates that 

 the reaction must involve a molecular electron orbit which encompasses 

 more than an iron atom. 



SUMMARY 



The reactions of beef liver catalase with H2O2 have been studied under 

 conditions of varying temperature, dielectric constant and viscosity of 

 the suspending medium. These studies have shown that the rate ki at 

 which beef liver catalase combines with HoOl. to form the intermediate 

 compound is temperature independent from 5° to 45°C, not appreciably 

 altered by the dielectric constant, but dependent on diffusion rates if 

 these are lowered below 0.8 X 10~^ cm-/sec. The constant k4 , at which 

 the intermediate complex reacts with a second molecule of hydrogen 

 peroxide, is also little altered by variations in the dielectric constant, but 

 is dependent on temperature and diffusion rate. These results are in accord 

 with the prediction of the entropy of activation from absolute rate theory. 

 The results also indicate that any encounter with a portion of the molecu- 

 lar surface appreciably larger than an iron atom will be effective in pro- 

 ducing a reaction in the diffusion controlled range. 



