74 INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



is about 7. The fraction of denatured sites at any pH is proportional to 

 the upper curve of figure 1, and pressure decreases this fraction to the lower 

 curve, increasing the amount of native enzyme in the system and in- 

 creasing the observed rate. 



/ Pressure changes myosin activity then for two reasons. First, it in- 



I creases the relative number of native sites. Second, it decreases the rate 



I of splitting by each active site. Hydroxyl ion has the opposite effect in 



j both cases. At low pH, nearly all sites are active at atmospheric pressure, 



1 the decreased rate of splitting predominates, and pressure decreases the 



observed rate of hydrolysis. At high pH, relatively few sites are native 



at atmospheric pressure, the pressure increase in the number of native 



sites more than makes up for the decreased rate of splitting per native 



i site, and pressure increases the observed rate. 



According to the usual Michaelis-Menten treatment, the rate, v, is 



V = 



Kn, + (S) 



At high substrate concentration, v = V = ko (E). If the enzyme is re- 

 versibly denatured and only the native form is active, the concentration 

 of native enzyme (number of active sites) must be substituted. If 



^, (Eden)(H+) 



K = 



(HEnat) 



then 



_ ko(Etotai) const-T X (Etotai) X e'^^*'-^-^ 



^ ^ oF) ^ "^ (H+) 



This formula is used throughout. 



At constant temperature and enzyme concentration, where only the 

 pressure varies, the ratio of the rate at pressure p to the rate at atmospheric 

 pressure is 



g-pAV*/RT 



Koe-p^ 



V*/RT / Ko \ 



+) V (H+) / 



*/RT 



1 _|_ ° Q-p^V*IRT 



1 , J^ (H+) 



(H+) 



if Ko is the value of K at atmospheric pressure. It is convenient to define 



