FACTORS INFLUENCING B VITAMIN REQUIREMENTS 



293 



and a heat-stable, dialyzable fraction (possibly manganese), and catalyzes 

 the overall reaction: 



CH 3 

 N=C— NH 2 C=C— CH 2 CH 2 OH 



CH 3 — C C CH 2 ±N 



N— CH 



ci- c— s 



N=C— NH 2 



-i L 



CH 3 



C=C— CH 2 — CH 2 OH 



that is, 



CH 3 — C C CH 2 OH + N 



R'CH 2 N+R 3 + H 2 =± R'CH 2 OH + NR 3 + H J 



+ H- 



The reaction is somewhat unique in that a hydrogen ion is formed in the 

 process. Studies of the reaction employing enzyme extracts yield unidenti- 

 fied pyrimidine derivatives, while the pyrimidylmethyl alcohol is only 

 obtained by using whole tissue suspensions. Whereas a number of o-amino 

 derivatives of aromatic compounds are able to inhibit this reaction, m- 

 substituted compounds generally activate it. This activation by substances 

 such as ?n-nitroaniline and m-aminobenzoic acid is believed to occur by 

 virtue of a combination between the ra-amino group of the accelerator and 

 the 5-methylene group of the pyrimidine moiety as it is split off. When 

 ra-nitroaniline is used as the accelerator (or acceptor) for instance, it is 

 possible to isolate from the reaction mixture N-(2-methyl-6-amino- 

 pyrimidyl-5-methyl) -m-nitroaniline. Presumably the enzyme itself cata- 

 lyzes only the first reaction, a sort of transmethylation in which the 

 methyl group is substituted with a pyrimidine derivative, and in which 

 the substituted methyl group is transferred from a quaternary amine to 

 a primary amine. Subsequent reactions in vivo then hydrolyze the sec- 

 ondary amine formed to the pyrimidylmethyl alcohol. 159 * The enzyme is 

 of additional interest in that it rapidly destroys the thiamine in dead 

 carp, unless the enzyme is inactivated by immediate heating after death. 

 Employing known bioassay techniques (p. 283), it has been found that 

 42 per cent of a test dose of 7.5 mg of thiamine (and 50 per cent of the 

 thiamine in the basal diet) is destroyed by the consumption of 100 gm.of 

 raw clams. 100 The anti-thiamine activity of a large variety of plant mate- 

 rials has been shown to be due to nonenzymatic factors, and the "Chastek 

 factor" remains the principal example of enzymatic B vitamin destruction. 

 Inactivation of B Vitamins by Binding Agents. In 1916 1G0 Bateman 



