50 CHOLINE 



this organism. It was found that the active compounds contained N — C — • 

 C — OH and N — C — C — C — OH linkages. Substitution of, or through, the 

 hydroxyl group resulted in complete inactivation of the molecule. Amino- 

 ethanol, monomethylaminoethanol, and dimethylaminoethanol were among 

 these substances supporting the growth of the organism. The activity of 

 triethylcholine, diethylaminoethanol, and similar compounds plus the in- 

 activity of betaine, methionine, and other compounds containing labile 

 methyl groups indicated that the role of choline in pneumococcal metabo- 

 lism is not that of transmethylation. The fact that aminoethanol is required 

 in ten times the concentration of choline for equivalent growth suggested 

 that choline is not demethylated to give ethanolamine. 



In contrast to the pneumococcus, two genetically different strains of 

 Neurospora crassa are unable to utilize aminoethanol in place of choline.'* 

 These mutants are designated as strain 34486, or cholineless-1 , and strain 

 47904, or cholineless-2 . Each strain is believed to carry a mutation of a 

 different single gene concerned with the synthesis of choline,^ and each 

 strain attains a growth rate comparable to that of the wild type in choline- 

 supplemented media. The following compounds show some activity for both 

 mutants: choline, dimethylaminoethanol, monomethylaminoethanol, ace- 

 tylcholine, arsenocholine, phosphorylcholine, dimethylethylhydroxyethyl- 

 ammonium chloride, diethylmethylhydroxyethylammonium chloride, tri- 

 ethylcholine, and methionine. The following compounds are inactive for 

 both mutants: aminoethanol, betaine, creatine, sarcosine, neurine, diethyl- 

 aminoethanol, dimethylamine, trimethylamine, and tetramethyl ammonium 

 chloride.'' ^•''•^ The work of Horowitz^ showed that an inherent difference 

 exists between the two cholineless mutants of Neurospora in their ability 

 to utilize monomethylaminoethanol and dimethylaminoethanol. The results 

 suggested that the gene-controlled deficiency in cholineless-2 may be con- 

 cerned with the methylation of a mono- or dimethylated precursor of 

 choline, whereas that in cholineless-1 blocks a prior step in the synthesis. 

 It was observed that cholineless-2 produces a substance which is inactive 

 for itself but which promotes the growth of cholineless-1. The substance 

 has been isolated from the cultures of cholineless-2 and identified as mono- 

 methylaminoethanol. This substance is therefore a normal intermediate in 

 the synthesis of choline in Neurospora. According to Horowitz, in choline- 

 less-1 the genetic block precedes monomethylaminoethanol, so that the 

 mutant cannot synthesize this intermediate but can utilize it for choline 

 synthesis if an exogenous supply is available. In cholineless-2 a partial 

 block exists between monomethylaminoethanol and choline. This mutant 



7 T. H. Jukes, A. C. Dornbush, and J. J. Oleson, Federation Proc. 4, 157 (1945). 



8 T. H. Jukes and A. C. Dornbush, Proc. Soc. Exptl. Biol. Med. 58, 142 (1945). 



9 N. H. Horowitz, J. Biol. Chem. 162, 413 (1946). 



