KARL F. GUTHE 



75 



V'p = Vpe+ <pAv*/RT)_ 'Pl-jjg jg equivalent to a vertical shift of a logarithmic 

 curve. Then 



V, 



- 1 = 



. Cl _ p-pAV/RT) °- p-pAV/RTCe+pAV/RT _ 1) 



(H+) ^ ' (H+) ^ ^ 



1-1 ? p-pAV/RT 



1 -L J^ e-P'^V/RT 



+ (H-)' 



Since Ko e-P^^/^'^ = Kp , 



Yz: _ 1 = Kp 

 V (H+) + Kp 



(g+pAV/RT _ 1)^ 



This is a Henderson-Hasselbalch curve in shape, with the maximum 

 ordinate equal to (e?^^/^^ — 1). The midpoint is pKp . 



CALCIUM EQUILIBRIUM 



The preceding experiments were carried out at a constant concentra- 

 tion of calcium ions. The dependence of the pressure effect on pH might 



2 3 ^0 I 2 



Fig. 2. Dependence of myosin ATP-ase activity on calcium concentration (4). 

 Left: activity-concentration curves are the same shape at different temperatures. 

 Right: activity-concentration curves are the same shape at different pressures. 



simply reflect its dependence on calcium concentration, since calcium ac- 

 tivates myosin ATP-ase. The calcium equilibrium cannot, however, be 

 the active-inactive equilibrium we have considered. If the equilibrium 

 constant for the calcium equilibrium were sensitive to temperature and 

 pressure, as that for the hydrogen ion equilibrium is, the ATP-ase activity 

 should reach half its maximum value at a calcium concentration that de- 

 pends on temperature and pressure. Instead, it is unaltered by temperature 

 (fig. 2) and only slightly changed, if at all, by pressure. The ATP-ase 



