32 II. DIGESTION AND ABSORPTION OF FATS 



homologues. 199 L6vy and Tchoubar 199 showed that methyl-2-propionyl- 



choline, CHsCHCC^COOCHaCH^CCHaMOH), is hydrolyzed by the e 



enzyme, while butyrylcholine, CH 3 CH 2 CH 2 COOCH 2 CH 2 N(CH 3 )3(OH), is 

 not hydrolyzed. The latter substance is considered to be an inhibitor of 

 the enzyme, as are also methyl-3-butyrylcholine, CH 3 CH(CH 3 )CH 2 - 



COOCH 2 CH 2 N(CH 3 ) 3 (OH), and ethyl-2-butyrylcholine, CH 3 CH 2 CH(C 2 H 6 ) 



COOCH 2 CH 2 N(CH 3 ) 3 (OH). 



p-Cholinesterases were shown by Zeller et a/. 200 to be capable of catalyzing 

 not only the hydrolysis of ethoxyethanol acetate (C 2 H 5 OC 2 H 4 OCOCH 3 ), 

 but also that of desoxycorticosterone acetate (C 2 iH 2S 3 OCCH 3 ), keto- 

 propanol acetate (CH 3 COCH 2 OCOCH 3 ) and acetylsalicylic acid (HO- 

 C«H 4 COOCCH»). 



Drying greatly increases the resistance of cholinesterase e to organic 

 solvents 201 ; the lipids extracted by light petroleum ether or by acetone 

 were shown to be unessential for the functioning of the enzyme. The 

 optimum pH for stability of serum cholinesterase was reported by Gold- 

 stein and Doherty 2 " 2 as 6.0, which differs from the pH. of optimum activity, 

 8.5. It was found that thermal denaturation proceeded more rapidly at 

 low ionic strength than at physiologic salt concentration. The loss of 

 stability resulting from dilution could be prevented by the addition of 

 albumin, as well as by the addition of the reversible inhibitors, prostigmine 

 and methylene blue. It was also noted by these investigators 202 that the 

 thermal denaturation of the enzyme does not proceed as a first-order 

 reaction, but diminishes to a very great extent with time; this is not altered 

 by albumin. It is suggested that the active enzyme is stabilized by a 

 denatured enzyme, or by denatured impurities in the fractions employed. 

 Stadie et al. 203 found that cholinesterase was not destroyed by the applica- 

 tion of oxygen under pressure to its solution or of other oxidizing agents 

 such as o-iodosobenzoate. 



Cholinesterases from the yellow-banded krait (Bnngarus fasciatus) 

 were found to be heat-labile, since crude and purified preparations lost 

 their potency 204 after heating to 60-70°C. The reaction of cobra cholin- 



199 J. Levy and B. Tchoubar, Compt. rend., 231, 1262-1264 (1950). 



200 E. A. Zeller, G. A. Fleischer, R. A. McNaughton, and J. S. Schweppe, Proc. Soc. 

 Expt. Biol. Med., 71, 526-529 (1949). 



201 K". Bullock, Biochem. ./., 49, vii-viii (1951). 



202 A. Goldstein and M. E. Doherty, Arch. Biochem., 33, 22-34 (1951). 



203 W. C. Stadie, B. C. Riggs, and N. Haugaard, J. Biol. Chen., 161, 175-180 (1945). 

 20J B. N. Ghosh, Oesterr. Chem.-Ztg., 43, 158-163 (1940). 



