832 15. EFFECTS OF VARIOUS FACTORS ON INHIBITION 



that the principal effect was on the binding of the substrate to the enzyme. 



The salt concentration also affects the activation of the enzyme by Mg++ 

 and it is possible that this ion is involved in the binding of the substrate. 

 The activity of cytochrome oxidase from spinach and soybean also shows 

 a maximum as the concentration of NaCl is varied (Fig. 15-22) (Miller and 



50 



(BICARBONATE)or(NaCI) 



100 



150 



200 

 mM 



Fig. 15-22. Effects of bicarbonate (dashed curves) and NaCl (solid 



curves) on cytochrome oxidase from spinach (A and C) and soybean (B 



and D). (From Miller and Evans, 1956.) 



Evans, 1956). Sodium bicarbonate inhibits this enzyme and part of this 

 effect is due to the Na+, the true inhibition produced by the bicarbonate 

 being the difference between the curves. This is a good illustration of the 

 need for correction when the ordinary physiological ions have effects on the 

 enzyme. 



Summarizing the effects observed on various enzymes, it is evident that 

 increasing ionic strength can either decrease, increase, or fail to affect 

 the rate, and that in many cases a biphasic action is evident, i.e., an increase 



