VI. BIOGENESIS 



51 



can synthesize monomethylaminoethanol l)ut is unable to convert it to 

 choline at the normal rate; as a result, the intermediate accumulates in the 

 culture. Hypothetical intermediates are bracketed, and vertical dotted 

 lines indicate points of blocking in the following scheme proposed by 

 Horowit z . 



Clioline 



Challenger and coworkers^" '^- showed that trimethylarsine is one of the 

 volatile odorous products evolved from mold cultures containing arsenious 

 acid. The mold Scopnlanoj^sis hrevicaulis not only methylates arsenite but 

 also converts selenite^^ and tellurite^^ to the respective dimethyl derivatives. 

 Challenger and Higginbottomi° suggested that choline or betaine might 

 supply methyl for these methylations. A means of separation and identifi- 

 cation of aminoethanol, devised by Simons,'^ failed to show an accumula- 

 tion of this possible demethylation product of choline in a culture of S. 

 hrevicaulis containing added choline and arsenite. No evidence was ob- 

 tained for the methylation of sulfur compounds by this organism except 

 by fission of dialkyl disulfides. ^^^ '^ However, dimethyl sulfide was isolated 

 as a product of the fungus Schizophyllum commune Fr}'^ Smith and Schlenk 

 obser\'ed that thiomethyladenosine accumulated in yeast grown in a me- 

 dium containing an excess of methionine but not of sulfate, homocystine, 

 cysteine, or glutathione. The nucleoside was used by the yeast as a source 

 of sulfur if added to a deficient medium. ^^ 



Although the Neurospora studies suggest similarity in the biogenesis of 

 choline between animals and microorganisms, there is little evidence that 

 degradation of choline proceeds along the same pathways. Trimethylamine 

 is the usual product, and its formation has been noted in choline-containing 



10 F. Challenger and C. Higginbottom, Biochem. J. 29, 1757 (1935). 

 " F. Challenger, C. Higginbottom, and L. Ellis, J. Cheiu. Soc. 1933, 95. 



12 F. Challenger and A. A. Rawlings, J. Chem. Soc. 1936, 264. 



13 F. Challenger and H. E. Xorth, ./. Chem. Soc. 1934, 6S. 



1^ AI. L. Bird and F. Challenger, ./. Chem. Soc. 1939, 163; 1942, 571, 574. 



'5 C. Simons, Biochem. .1 . 35, 749 (1941). 



i« F. Challenger and S. Blackburn, J. Chem. Soc. 1938, 1872. 



17 F. Challenger and P. T. Charlton, ./. Chem. Soc. 1947, 424. 



18 J. H. Birkinshaw, W. P. K. Findlay, and P. A. Webb, Biochem. J. 36, 526 (1942). 

 1^ R. L. Smith and F. Schlenk, Federation I'roc. 11, 289 (1952); Arch. Biochem. and 



Biophus. 38, 159, 167 (1952). 



