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J. TIBBS 



reversible nature of the effect. In 1 mM MgCl 2 , 1.25 raM EDTA re- 

 duced the enzyme activity to about 25% of its original value and 2.5 

 mM EDTA lowered it still further to about 10%. On the other hand, 

 increasing the concentration of MgCl 2 above that of the EDTA pro- 

 duced a rapid increase in activity to give approximately the same max- 

 imum value in each case. By altering the magnesium to EDTA ratio, 

 the enzyme could therefore be activated or inhibited as required. 



The use of turbidity measurements for showing changes in the wa- 

 ter content of mitochondria has been described by Cleland (1952). If 

 transparent particles, suspended in water, are made to absorb water, 

 then their refractive index approaches that of water, scattering of 

 light is reduced, and the turbidity of the suspension is lowered. 



Figure 3 shows the effect on the optical density at 520 m/x of activat- 



60 



TIME IN MINUTES 

 Fig. 3. Change in optical density at 520 im*, with time (room tempera- 

 ture throughout) after mixing perch sperm tails with MgCl 2 and ATP. 

 Each cuvette contained the same quantity of flagella in standard sucrose- 

 tris solution, and final suspensions were also 1.6 mM with respect to EDTA. 

 # , no MgClo , no ATP; ±, 5 mM MgCl, , no ATP; ■ no MgCl 2 , 2 mM 

 ATP; O. 5 mM MgCL , 2 mM ATP. " 



