40 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



attributed to either ki or k^ without direct studies of the effect of tempera- 

 ture upon the intermediate compound. This has been carried out in detail 

 in Beers and Sizer (4) and their vakies of aE and AS are given in table 1. 



RATE OF FORMATION OF INTERMEDIATES 



Gibson and Roughton have studied the effects of temperature upon the 

 rate of formation of intermediates of hemoglobin with its various ligands, 

 and a complete summary of such data is given in figure 2 (7). 



In the case of catalase and peroxidase, the rapid flow method has been 

 used to determine the reaction velocity constant for the combination of 

 enzyme and substrate at room temperature. Since the expenditure of 

 enzyme for such studies is rather great, no detailed data are available on 

 the effect of temperature, although in a preliminary study of the effect of 



temperature upon the reac- 

 Table 1. Experimental energy, free energy and tion of peroxidase and hy- 



ENTROPY OF ACTIVATION OF THE TWO REACTIONS, drogcii pcroxide, a vciy low 



value has been reported 

 (12). More recently, Ack- 

 erman has made a detailed 

 study of the catalase reac- 

 tion and his results are in- 

 cluded elsewhere in the 

 symposium (13). 



A reaction of great phys- 

 iological and chemical in- 

 terest is that of oxygen with 

 the reduced cytochrome as . 

 This reaction proceeds so rapidly at room temperature that it is necessary 

 to study it at low temperatures in order to obtain measurements over a 

 reasonable range of oxygen concentrations. For isolated particles, a value 

 of 10" M~^ sec.~^ has been obtained at 3°. Preliminary data (14) on the 

 effect of low temperatures on this interesting reaction show that an inter- 

 mediate between cytochrome 03 and oxygen })ecomcs rate limiting as the 

 temperature is lowered to —10°. 



STEADY-STATE METHOD 



It has recently been possible to devise an equation from which the veloc- 

 ity constant for the combination of enzyme and substrate can be com- 

 puted directly from the kinetics of the intermediate compound (16) with- 

 out the necessity for measuring very short times required by the procedure 

 described above. The measurement depends only upon the concentration 

 of the enzyme substrate compound in the steady state and the 'half-life' 



Data of Beers and Sizer 

 from J. Phys. Chem (4). 



on ki and ki . Data 



