ROBERT A. ALBERTY 



who find quite different effects at different pH values. Below 

 pH. 1 the concentration of buffer containing sodium maleate and 

 other added salts is without effect on the activity over a 1000- 

 fold range. At />H 7.0 and 7.5 the activity decreases slightly 

 with increasing electrolyte concentration, and at /?H 8.9 the 

 effect is much greater. The effects are represented quite well by 

 a form of the Debye-Hiickel equation. 



In the case of fumarase widely different results are obtained 

 in different buffers of the same /?H and ionic strength. Since 

 the Michaelis constants for fumarase determined in phosphate 

 buffer are a linear function of phosphate concentration, phos- 

 phate appears to be a competitive inhibitor. However, the situ- 

 ation is more complicated than this, since the maximum initial 

 velocity also depends upon phosphate concentration. Since 

 monovalent and divalent phosphate ions have quite different 

 activating and inhibiting effects and the ratio of the concentra- 

 tions of these ions changes with /?H, the dependence of the 

 kinetic constants upon />H in phosphate buffers is extremely 

 complicated. 



THE HALDANE EQUATION 



If there are appreciable concentrations of both products and 

 reactants at equilibrium so that the kinetics of the catalysis of 

 both the forward and reverse reactions may be studied, it is pos- 

 sible to verify certain conclusions about the mechanism. The 

 kinetics of the forward and reverse reactions are not independent, 

 and Haldane (8) was the first to show that for a reaction like 

 (13) the maximum initial velocities and Michaelis constants for 

 the forward and reverse reactions are related to the equilibrium 

 constant for the over-all reaction in the same medium by 



^ _ (M),q _ Ff^m ,.qv 



where Fp and K^ are the maximum initial velocity and Michaelis 

 constant for the forward reaction and V^^ and K^ for the reverse 

 reaction. If there were activation or inhibition by substrate, 



580 



