290 G. ASHWELL, Z. DISCHE VOL. 4 (1950) 



are least affected. It is very significant that this sequence in the susceptibility to inhi- 

 bitory effects is the same for all kinds of ions and the reactions affected are of very 

 different tjrpes. The oxidation of glucose, for example, is as was shown due to two 

 completely different reactions. It appears most improbable that so many and so different 

 reactions should be influenced in the same way by all the ions. We have rather to assume 

 that the ions exert their influence on a substrate the activity of which is again correlated 

 is some way with the activities of all the enzymes of the oxidative system. Such a 

 substrate for example is the cytochrome system, which serves as Hg carrier to the oxida- 

 tion of the preformed substrates of the hemolysate as well as that of added glucose. 

 It seems impossible, however, to consider the cytochrome system as the point of attack 

 in the ionic inhibition, because of the great differences between various enzymes in their 

 sensitivity towards the ions. M/iooo of Ca almost completely inhibits the oxidation 

 of glucose, but the inhibition of the basic respiration of the hemolysate is not complete 

 even at M/200. M/500 HCN, on the other side, inhibits both to the same extent. All 

 this suggests that the inhibitory action of ions is directed against one single substrate 

 which in changing its physicochemical properties influences in its turn all the enzymes 

 of the oxidative system. The enzymes are in fact not in solution inside the cell, but are 

 attached to insoluble particles, the mitochondria. These contain, apart from proteins, 

 considerable amounts of lipids and ribosenucleic acids. In these subcellular structural 

 and functional units the enzyme proteins are probably attached to a stroma consisting 

 of lipo- and nucleoproteins and may be surrounded by a surface membrane. One way 

 to explain the effects of ions on the oxidative processes would therefore be to assume a 

 decrease in the permeability of such a surface membrane under their influence. The fact 

 that the aerobic glycolysis coupled with the oxidations is quite generally more stiongly 

 inhibited than the oxidative processes themselves is in agreement with this concept. 

 This glycolysis depends on the coupled phosphorylation of a phosphate carrier which 

 transfers the phosphate to glucose. Any decrease in the permeability of the surface 

 membrane will decrease the speed of the penetration not only of the substrate but also 

 of the phosphate carrier and the speed with which it leaves the particle after being 

 phosphorylated. The amounts of the phosphate carrier available for the reaction with 

 glucose must decrease to a much higher degree than the corresponding oxidative 

 process. It could also be that the ions change not the permeability but the physical 

 properties of the hypothetical stroma to which the enzyme proteins are attached. Any 

 change in the water binding capacity or shape of the protein molecules of the stroma 

 would have a considerable influence on the shape and arrangement of the respective 

 enzyme proteins and tend to change their activity. 



If we assume that in one way or the other the proteins of mitochondria are the 

 point of attack of inhibiting ions the most probable mechanism of this inhibitions appears 

 to be elimination of local electric fields on the surface of this protein, due to the ad- 

 sorption of the ions. Thus CNS"" which forms stable complexes with proteins, inhibits 

 the aerobic glycolysis at low concentrations, whereas CI"" is ineffective. This can also 

 explain the characteristic sjmergy between cations and anions in their effects. Even 

 at the isoelectric point of a protein the charged groups on its surface will exert con- 



* More recent experiments on the mechanism of the inhibition of the oxidative enzymes by Ca"*""*" 

 suggest, that the specific protein in the mitochondria, affected by ions, influences the energy transfer 

 during the enzymereactions of the Krebs cycle rather, than the enzymes themselves or the access 

 of substrates. The results of these new experiments will be reported in a subsequent paper. 



References />. 2g2. 



