898 ' 7. MERCURIALS 



Comparison of Effects of Hg++ on Intact Diaphragm and Homogenates 



The endogenous respiration of diaphragm homogenates fortified with ATP 

 was claimed by Demis and Rothstein (1955) to be inhibited faster and less 

 potently than the respiration of intact diaphragm by Hg++. Actually, from 

 the data given, it is not evident that the rate of inhibition in homogenates 

 is much faster; at 10 min after adding Hg++, for example, there is no sig- 

 nificant difference in the rates judged from the points presented, although 

 from then on the rate in intact diaphragm falls off, so that the inhibitions 

 are not equivalent again until 50 min. It was stated that it requires 10 

 times the concentration of Hg++ to inhibit homogenate respiration compar- 

 ed to intact tissue [in a later review Rothstein (1959) stated 200 times], 

 but no data on this point are given (the only experiment reported is with 

 the extremely high concentration of 9 m.M), and in any case it depends 

 on what time is chosen to compare the inhibitions (e.g., up to 50 min, 

 homogenate respiration is inhibited more strongly by 9 mM Hg++). It is, 

 furthermore, very difficult to interpret differences in inhibitions of intact 

 cells and extracts, since the substrates utilized, the pathways taken, and 

 the states of the enzymes are probably very different. Mercurial inhibition 

 has usually been found to be more potent in cell extracts than intact cells, 

 e.g., Nakayama (1959) reported that while 0.077 mM p-MB inhibits ethanol 

 oxidation 9% in Acetobacter, it requires only 0.0077 mM to inhibit 14% in 

 extracts. How much role the membrane plays in any of these observations 

 is impossible to determine. 



Binding of Hg++ to Yeast Cells and Loss of K+ 



The efflux of K+ from yeast is accelerated by Hg++ as it is from most 

 cells. Although the effects of the mercurials on permeability and active 

 transport will be taken up later, the work done by Rothstein and his co- 

 workers will be treated here since it has bearing on the concept of differen- 

 tial membrane binding. Rothstein and Bruce (1958) studied the efflux of 

 K+ into a K+-free medium flowing through a yeast cell column; since the 

 pH of the medium was 3.5, and lowering the pH enhances the efflux rate, 

 it was assumed that the process is mainly a K+-H+ exchange. The loss of 

 K+ from the cells is very sensitive to Hg++, 0.001 mM producing a slight 

 effect after a long lag period, and 0.003 mM producing at least a tripling 

 of the rate; at the highest concentration used, 0.1 mM, 80% of the cell K+ 

 is lost in 1 hr.* Passow and Rothstein (1960) used a different technique in 

 that the rate of K+ loss into a medium (distilled water adjusted to pH 3 

 with HCl) from a suspension of yeast cells was measured. The minimal ef- 

 fective concentration of Hg++ to accelerate the efflux was found to be 0.2 



* Dr. Rothstein informed me that Fig. 6 of the paper by Rothstein and Bruce 

 (1958) presents the cumulative K+ loss rather than the rate of K+ loss as stated. 



