ENZYMES CONCERNED WITH DIGESTION OF LIPIDS 45 



ethyl propionate, and benzoyl choline. 255 This is the same order in which 

 the cholinesterase of the red blood cells is able to split the esters. 256 On the 

 other hand, the hydrolytic products of acetylcholine in amounts up to 

 1.5 X 10 -2 M had little or no effect on the rate of hemolysis of the red 

 blood cells of the dog. 255 It is concluded that a remarkable correlation 

 exists between the activity of the enzyme and the ability of the cell to 

 maintain its selective permeability. 



In a further study of this problem, Holland and Greig 257 reported that 

 changes in permeability occurred only when the inhibitors (eserine, prostig- 

 mine, caffeine, and choline) were present in sufficient amounts to produce 

 at least a 50% inhibition of the activity of the cholinesterases. Under 

 these conditions, the resistance of the dog erythrocytes to hemolysis could 

 be considerably increased by the addition of acetylcholine in amounts of 

 10~ 2 to 10~ 5 M; the magnitude of the effect varied directly with the con- 

 centration of the drug. Holland and Greig 258 later showed that the Na + in 

 the rabbit erythrocyte is controlled by the acetylcholine-cholinesterase 

 system in the same way as K + is regulated in the dog and cat erythrocytes 

 by this system. In the rabbit, Na + largely replaces K + in the red blood 

 cells. It was also reported that inhibition of the cholinesterase system with 

 eserine increases the permeability of the rabbit erythrocyte to Na+. The 

 diffusion of potassium ions in dog and cat blood cells 258 and in human eryth- 

 rocytes 259 is likewise controlled by the cholinesterase system. 



In addition to the effect of cholinesterase on the permeability of blood 

 cells, similar relationships have been reported in other tissues. Thus, 

 Holland et al. 2eo noted that changes in the rate of metabolism of acetyl- 

 choline by cholinesterase may be correlated with changes in the permea- 

 bility of isolated guinea pig auricles to K + and Na + . The hydrolysis of 

 acetylcholine was shown to be accompanied by the release of K + from the 

 guinea pig auricle; the K + lost was replaced by Na + . Potent inhibitors 

 of cholinesterase partially or completely reverse the effect of acetylcholine, 

 depending upon the concentration of substrate employed. 



In a later publication, Greig et al. 261 demonstrated that the potassium 

 could be replaced in both dog and human erythrocytes against a concen- 



255 M. E. Greig and W. C. Holland, Am. J. Physiol, 164, 423-427 (1951). 

 286 D. H. Adams, Biochim. et. Biophys. Acta, 3, 1-14 (1949). 

 267 W. C. Holland and M. E. Greig, Arch. Biochem., 32, 428-435 (1951). 

 288 W. C. Holland and M. E. Greig, Am. J. Physiol, 162, 610-615 (1950). 



259 P. E. Lindvig, M. E. Greig. and S. W. Patterson, Arch. Biochem., 30, 241-250 (1951). 



260 W. C. Holland, C. E. Dunn, and M. E. Greig, Am. J. Physiol, 16S, 546-556 (1952). 



261 M. E. Greig, J. S. Faulkner, and T. C. Mayberry, Arch. Biochem. Biophys., 43, 

 39-47 (1953). 



