RIBOFLAVIN 



679 



Flavin-adenine-dinucleotide prevents the toxicity of the diamino- 

 phenazine for Lactobacillus casei in a manner analogous to riboflavin, 

 and is equally effective. 31 



Atebrin, Quinine and Related Antimalarials. The discovery that ate- 

 brin inhibits the oxygen consumption of various organisms resulted in 

 investigations of possible relationships to the riboflavin coenzymes. 58, 59, 60 

 It was demonstrated that atebrin inhibits D-amino acid oxidase 60 and 

 prevents the combination of the apoenzyme of cytochrome reductase 

 with riboflavin-5'-phosphate. 61 Although riboflavin-5'-phosphate at a 



CH 3 



CH 



CH 2 CH 2 CH— CH=CH 2 



I I I 

 HOCH— CH CH 2 CH 2 



/ 



quinine 



CH 3 



CH 3 



C 2 Hg 



NH— CH— CH 2 — CH 2 — CH 2 — N 

 I \ 



I C 2 H 6 



atebrin 



ratio of 1 to 500 prevents the inhibitory action of atebrin, the inhibition 

 resulting when atebrin is added to the apoenzyme of cytochrome reduc- 

 tase prior to the coenzyme is not affected by the coenzyme. 61 



A study of the effect of a number of compounds on the D-amino acid 

 oxidase system has revealed that a large number of compounds related to 

 quinine and atebrin inhibit the enzyme. 02 Since increased concentrations 

 of flavin-adenine-dinucleotide prevent the inhibition resulting from a 

 number of these compounds, competitive inhibition is indicated. The rela- 

 tive activities of these compounds as compared with quinine at two dif- 

 ferent temperatures are indicated in Table 40. Atebrin, auramine, and 

 novalauramine are somewhat more effective than quinine, while plas- 

 mochin and a number of quinoline derivatives are approximately as 



