IV. BIOCHEMICAL SYSTEMS 39 



of choline oxidase activity. ^^^ The oxidase system was not influenced by a 

 deficiency of vitamin B]2 in the chick'^^ or by thiamine/" vitamin E/^" or 

 histidine^*^ deficiency in the rat. Intraperitoneal injection of urethane as 

 well as x-irradiation of mature hens reduced the bone marrow choline oxi- 

 dase. ^^^ Whole body x-irradiation of adult male rats with a dosage of 200 

 r. appeared to decrease liver choline oxidase activity, but the effect was 

 uncertain in view of the marked increase in endogenous respiration.'^^ The 

 enzyme was poisoned by high oxygen tensions, probably due to its depen- 

 dence on its sulfhydryl groups. '^^ The injection of thyroxine had no effect 

 on the oxidase activity of the rat.'^^ 



Swendseid et al.^^^^ showed that the feeding of ethionine (S-ethylhomo- 

 cysteine) to rats decreased the choline and sarcosine oxidases but not the 

 succinoxidase of the liver. This possible antagonist of methionine also 

 inhibited choline and sarcosine oxidases in vitro in homogenized prepara- 

 tions, but the effect was absent if the preparation was dialyzed before its 

 addition. Neither methoxinine nor methionine sulfoximine inhibited choline 

 oxidase in the in vitro studies. 



In summarizing the discussion of "choline oxidase," it is pertinent to 

 emphasize that, with few exceptions, the term has not referred specifically 

 to either of the dehydrogenases that convert choline to betaine aldehyde 

 and the aldehyde to betaine but has included the system responsible for the 

 transport of protons and electrons through the cytochromes to oxygen. 

 The two dehydrogenases appear to be different enzymes, although both 

 occur in liver mitochondria. They may be separated on the basis of the 

 greater solubility of the betaine aldehyde dehydrogenase.'^^'' Each is esti- 

 mated by the anaerobic reduction of ferricyanide in the presence of the 

 respective substrate, choline or betaine aldehyde. Strength et al.^^'"^ believe 

 that both enzymes are DPN-linked, although the necessity of DPN for 

 the action of choline dehydrogenase has been questioned.'^" Folinic acid'^" 

 and riboflavin''^^' '" appear essential for the dehydrogenation of choline. 

 Ebisuzaki and Williams'*^" demonstrated the importance of flavin adenine 

 dinucleotide (FAD) for liver choline oxidase activity, especially in prepara- 



'8 M. B. Gillis and R. J. Young, Poultry Sci. 30, 468 (1951). 



^9 E. Egana, Pubis, lab. rued, exptl. din. med. Univ. Chile 1, 127 (1946). 



8» E. L. Hove and J. O. Hardin, Proc. Soc. Exptl. Biol. Med. 78, 858 (1951). 



81 J. W. Bothwell and J. N. Williams, Jr., J. Biol. Chem. 191, 129 (1951). 



82 J. S. Dinning, I. Meschan, C. K. Keith, and P. L. Day, Proc. Soc. Exptl. Biol. 

 Med. 74, 776 (1950). 



83 H. O. Kunkel and P. H. Phillips, Arch. Biochem. and Biophys. 37, 366 (1952). 



84 F. Dickens, Biochem. J. 40, 171 (1946). 



85 R. L. Smith and H. G. Williams-Aahman, Nature 164, 457 (1949). 



85a M. E. Swendseid, A. L. Swanson, and F. H. Bethell, /. Biol. Chem. 201, 803 (1953). 

 ssb D. R. Strength, J. R. Christensen, and L. J. Daniel, J. Biol. Chejn. 203, 63 (1953). 

 8B<= K. Ebisuzaki and J. N. Williams, Jr., J. Biol. Chem. 200, 297 (1953). 



