NACHMANSOHN: CHEMICAL MECHANISM IN NERVES 405 



cholinesterase can hydrolyze other esters. Specificity, in this case, 

 would be expected on the basis of analogy to be only relative, not 

 absolute: Cholinesterase might be expected to split ACh at a higher 

 rate than other esters, whereas other esterases might be expected to be- 

 have differently. By testing a number of substrates, a pattern has 

 been obtained which makes it possible to distinguish specific cholin- 

 esterase from other esterases. ^^ 



In the variety of nerve tissues which have been used as basis for 

 establishing the new concept, the enzyme was found to be an esterase 

 specific for ACh: viz., mammalian brain, lobster nerve, squid fiber con- 



1001- 



lOO 75 2S 3 



I 16 



NUC 

 CAUD 



OX 



ACH PRO But me ben trib meBU 



^00 



a 00 



I 



KIDNEV 



GUINEA 

 PIG 



100 2m 371 6 200 108 28 



Figure 3. Pattern of cholinesterase (nucleus caudatus of ox) in presence of different substrates 

 compared to that of an esterase (kidney) not specific for acetylcholine. 



The columns represent the Q of the substrates, the Q of ACh being 100. Abbreviations: Pr = 

 propionylcholine, Bu = butyrylrholine, Me = acetyl -j8 -methyl choline (mecholyi), Be = benzoyl- 

 choline, Tr = tributyrin, Mb = methyl butyrate. 



taining the giant axon, and the electric tissue. All show a similar 

 pattern, typical for cholinesterase. Even then, rigid statements should 

 be avoided. Occasional deviations in one or the other directions may 

 be expected. Recent observations of Richards and Cutcomp^*' have 

 revealed that the cholinesterase of bee brain splits acetyl-/3-methyl- 

 choline at a higher rate than ACh, whereas, otherwise, the pattern was 

 typical for cholinesterase. In contrast, the hydrolysis patterns of the 

 esterase of other organs (liver, kidney, and pancreas) differ greatly 

 from that of cholinesterase (figure 3). The esterase in these tissues 

 shows several variations, but this could be expected, since the physio- 

 logical substrate is unknown, and probably varies in the different or- 

 gans. They should be referred to as unspecified, not as unspecific, 

 esterases, because they may well be specific for substrates not as yet 

 specified. ACh is metabolized at a high rate only in nerve tissue, 



