60 II. DIGESTION AND ABSORPTION OF FATS 



purified state by Rothenberg and Nachmansohn. 349 All the esterase in the 

 electric tissue appears to be cholinesterase. The cholinesterases of cobra 

 venom and of that of the yellow-banded krait (Bungarus fasciatus) have 

 been concentrated twenty-fold and eleven-fold, respectively, as judged by 

 the nitrogen content of the original and of the purified samples. 339,360 The 

 preparations of this enzyme from the Colubridae are among the most potent 

 hitherto known. Other preparations of cobra venom cholinesterase in- 

 clude those of Bovet and Bovet 351 and of Bovet-Nitti. 206 



(i) Acetylcholine in Tissues. A number of workers have made quantita- 

 tive estimates of the acetylcholine content of tissues. Marquardt and 

 Hirsch 352 reported a total of 1 to 4 jug- % of acetylcholine in ox blood, in 

 which it occurs mostly on the surface of the erythrocyte. Davis 353 noted 

 values of 10 to 70 /xg. % in human cerebrospinal fluid, with an average of 

 28 ng. %, which was approximately four times the concentration which he 

 found in normal blood serum. 



The amount of acetylcholine in the whole rat brain was found to remain 

 relatively constant after excision ; the quantity in the cortex decreased in 

 time. 354 Freezing in liquid air caused a considerable loss in acetylcholine; 

 this loss did not take place in tissues from eserinized animals. 354 



Virtually all acetylcholine in the brain is in the "bound" or combined 

 form. Acid, mechanical disturbance, freezing, suspension in hypotonic 

 solutions and medium and high K + concentrations accelerate liberation 

 from the bound form. 354 Mann, Tennenbaum, and Quastel 355 concluded 

 some years ago that the synthesis of acetylcholine takes place through the 

 intermediate formation of combined acetylcholine. The rate of formation 

 of this complex form of acetylcholine is more rapid than is that of free 

 acetylcholine. The rate of formation of the complex form was not found 

 to be increased in the presence of eserine, which prevents the destruction of 

 free acetylcholine. 355 The addition of potassium ions to eserinized respir- 

 ing brain tissue slices increased the rate of formation of acetylcholine, but 

 high concentrations of K + were inhibitory. An equilibrium was shown to 

 exist between the free and the combined forms. Potassium and ammonium 



349 M. A. Rothenberg and D. Nachmansohn, J. Biol. Chem., 168, 223-231 (1947). 



350 D. K. Chaudhuri, Science and Culture (Calcutta), 8, 238 (1942); Chem. Abst., 37, 

 1458 (1943). 



351 F. Bovet and D. Bovet, Ann. Inst. Pasteur, 69, 309-312 (1943). 



352 P. Marquardt and H. H. Hirsch, Z. physiol. Chem., 289, 131-153 (1952). 



353 J. E. Davis, Am. J. Physiol, 162, 616-618 (1950). 



364 K. A. C. Elliott and N. Henderson, Am. J. Physiol., 165, 365-374 (1951). 



385 P. J. G. Mann, M. Tennenbaum, and J. H. Quastel, Biochem. ./., 32, 243-261 (1938). 



