MITOCHOXDRIA. CELLS. AND TISSUES 



581 



but found u to vary with the concentration: u — 0.41 for 0.2 inM, 0.17 for 

 0.042 mM, and 0.07 for 0.01 mM. Actually, this equation assumes that the 

 inhibition will eventually be complete, whereas from the shapes of the 

 curves this does not seem likely. When equations of the type 12-1 and 12-3 

 are used and estimates are made of the probable final inhibition, a does 

 not vary as much with concentration: « = 0.66 for 0.2 mM, 0.38 for 0.042 

 mM, and 0.44 for 0.01 mM, with an average of 0.49 h"^. They posed the 

 problem as to whether the observed rate was due to the diffusion into 

 the tissue or to the reaction with the enzymes, and concluded from indirect 

 experiments that diffusion was relatively rapid (equilibrium achieved in 

 1-2 min) and that the results could best be explained on the basis of a 

 unimolecular reaction of HgCL, with the enzymes. They finally point out 

 that a disturbing factor is the reduction in HgCLj concentration due to bind- 



150 



TIME 



Fig. 12-25. Effects of heavy metal ions on the respiration of Aspergil- 

 lus. (Ag+) = 0.1 mM, (Cu++) = 7.5 mM, and (Hg++) = 0.2 mM. (From 

 Cook, 1926 a.) 



ing to the tissue; this would have certainly reduced the rate of inhibition 

 progressively, especially at the lower concentrations. 



(B) Effects of heavy metals on t/ie respiration of Aspergillus. An interest- 

 ing attempt to interpret inhibition rate curves was made by Cook (1926 a), 

 who found a variety of responses in the respiration of the mold, Aspergillus 

 niger, to the heavy metal ions (Fig. 12-25). One may notice immediately 

 that these rate curves indicate some differences in the mechanism of action 

 of these heavy metals. Many such differences between inhibitors are prob- 



