90 



INFLUENCE OF TEMPERATURE OX BIOLOGICAL SYSTEMS 



the main difference being that in the n3 fiber the curvilinear component 

 persists within the lower pH range. The tension in this fiber below jiH 6.8 

 thus depends on two separate mechanisms whose effects are additive and 

 which are influenced to a different extent by temperature. In effect, the 

 component that appears to be linear provides a base line upon which the 

 curvilinear component is superimposed. When this base line is taken into 

 account, the curvilinear component bears the same relation to temperature 

 throughout the entire pH range. Plotting logio [y/(l — yj] against the 

 reciprocal of the absolute temperature yields a straight line whose slope 



10 10 



TEMPERATURE 



30" C 



3 6yiO-* 



y-r 



Fig. 2. A : Tension in relation to temperature and pH in the glycerated psoas fiber. 

 B: Arrhenius plot of logm [y/(l — y)] for data of fig. 2A. 



indicates a AH of 36,000 cal. (fig. 2B-2). Since as shown in equation 2 

 the activated unit involves three active sites, the aH for the pK per active 

 site should be 12,000 cal. 



The dependence of the pK on temperature may be obtained directly by 

 plotting the pH at which half-tension occurs against the temperature. The 

 relation is linear, yielding a AH* of about 12,000 cal., which confirms 

 the above interpretation of the large AH of 36,000 cal. 



As mentioned in the preceding section, tension in nl fibers varies linearly 

 with temperature at pH 6.15 but in the usual curvilinear manner at 

 pH 7.0. It seems clear that quite different ]irocesses control the tension- 

 temperature relation at the two pH values. In addition, the fact of their 

 separation by small pH changes indicates a difference in their pK values. 

 Possibly the straight line relation represents an action of temperature on 



