HYDROLYSIS PRODUCTS OF PHOSPHOLIPIDS 241 



Although there is considerable support for the hypothesis that folic acid 

 is the coenzyme of CO, Williams'*'^ stated that the closely related folinic 

 acid (the so-called Leuconostoc citrovorum factor, LCF) is the actual co- 

 enzyme. However, synthetic; LCF was shown to have less effect upon the 

 CO system in vitro than did folic acid plus ascorbic acid. Williams^^ 

 obser\'ed that the activity of CO in vitro was reduced with a low vitamin C 

 concentration and increased with a high vitamin C content. According 

 to Williams, ^^ when aminopterin was fed to rats, liver ascorbic acid was 

 reduced to only 50% of normal. Although Mann et air* postulated that 

 hydrogen is transferred from CO to the cytochrome oxidase system, Wil- 

 liams and co-workers^* did not find that added cytochrome exerted any ef- 

 fect on CO activity. Williams et al.^^ demonstrated that a whole liver 

 homogenate furnished an adequate CO system for assay without addi- 

 tional co-factors. Normal rat liver has a choline oxidase activity equivalent 

 to 76.5 ul of O2 per ten min. per 167 mg. liver. '^ 



(c) Mechanism of Action of Choline Oxidase. Choline oxidase functions 

 by catalyzing the oxidation of choline to betaine according to the following 

 scheme : 



CHoCH,()H CH2CHO CHo— C=() 



I Choline oxidase | — H2O I I 



+ N > +N , +N ()— 



II! Ill K=o III 



(CH.O3 (CH3)3 (CH.O3 



Choline Betaine Betaine 



aldehyde 



The Oxidation of Choline to Betaine by Choline Oxidase 



Barrenscheen and Pantlitschko" reported that, in order to function as a 

 transmethylating agent, choline must be oxidized to trimethylamine oxide 

 ((CH3)3iN:0). Dubnoff^^ confirmed the fact that the oxidation of 

 choline must occur before it can function in transmethylation; the latter 

 worker suggested that it is converted to betaine rather than to trimethyl- 

 amine oxide. Thus, it would appear that the transfer of methyl groups 

 from choline is indirectly controlled by CO. Barrenscheen and v. Valyi- 

 Nagy^^ had demonstrated earlier in in vitro tests w^ith muscle, liver, brain, 

 kidney, and adrenal gland that a similar oxidation of methionine to a sul- 



^* J. N. Williams, Jr., /. Biol. Chem., 191, 123-127 (1951). 

 "* J. N. Williams, Jr., Proc. Soc. Exptl. Biol. Med., 77, 315-317 (1951). 

 '« J. N. Williams, Jr., G. Litwack, and C. A. Elvehjem, /. Biol. Chem., 192, 73-80 

 (1951). 



" H. K. Barrenscheen and M. Pantlitschko, Z. physiol. Chem., 284, 250-256 (1949). 



'8 J. W. Dubnoff, Arch. Biochem., 24, 251-262 (1949). 



" H. K. Barrenscheen and T. v. Vdlyi-Nagy, Z. physiol. Chem., 283, 91-99 (1948). 



