RIBOFLAVIN 673 



appears to depend on whether or not the test organism is able to effect 

 hydrolysis of a given ester. The tetra-acetyl derivative is almost as active 

 as riboflavin for rats, 27 but is inactive in the nutrition of Lactobacillus 

 casei and Bacillus lactis acidi 30 and as a coenzyme for the yellow 

 enzyme. 32 The triacetate derivative of riboflavin-5'-phosphate is also 

 inactive in the yellow enzyme test. 32 Riboflavin-5'-phosphate admin- 

 istered either orally or parenterally in the rat is fully as active as ribo- 

 flavin. 29 The sulfate of riboflavin shows some activity as a coenzyme for 

 the yellow enzyme. 32 Riboflavin mono-, di-, tri- and tetrasuccinates have 

 been prepared in the search for more soluble forms of the vitamin. 47 For 

 Lactobacillus casei, the latter two are essentially inert, whereas the first 

 two are respectively 60 and 18 per cent as active as riboflavin. For the 

 rat, the activities on a molar basis are 100, 65, 21 and per cent, respec- 

 tively, of riboflavin. The inactivity of the tetrasuccinate contrasts with 

 the high activity reported for the tetracetate in replacing riboflavin for 

 the rat. 47 



Both the mono- and diacetone derivatives of riboflavin are active in 

 the nutrition of rats. 25 - 27 However, the condensation of riboflavin with 

 chloral and with levulinic acid produced acetals which are inactive for 

 both Lactobacillus casei and the rat. 47 



The reaction of riboflavin with formaldehyde produces methylol deriva- 

 tives which are more soluble in water than the vitamin. The mono- 

 methylol derivative retains approximately 55 per cent of the activity of 

 the vitamin but polymethylol derivatives are much less active. 48 



2-Amino-4,5-dimethyl-r-D-ribitylaminobenzene increases the response 

 of Lactobacillus casei to suboptimal concentrations of riboflavin, but 

 alone at concentrations of 20 to 40 y per cc, it is 0.003 per cent as effective 

 as riboflavin. 31 In the presence of alloxan, the activity is increased to as 

 high as 0.35 per cent that of riboflavin. Alloxan alone is inactive, and 

 neither riboflavin nor flavin-adenine-dinucleotide affects this transforma- 

 tion. It is suggested that the organism has some slight ability to com- 

 bine these two components to form riboflavin. 31 



It has been reported that isoxanthopterincarboxylic acid, 2-thio-6- 

 hydroxypteridine, or lumazine can replace riboflavin or thiamine, or both, 

 in preventing changes in chronaxia in rats. 49 In similar experiments with 

 pigeons, isoxanthopterin, 6-hydroxypteridine, 2,6-diaminopteridine, 

 leucopterin, or lumazine are reportedly active in replacing riboflavin or 

 thiamine. 49 



Inhibitory Analogues of Riboflavin 



Although a number of analogues of riboflavin have been prepared, only 

 a few appear to inhibit specifically the functioning of riboflavin in 

 biological systems. These and related inhibitors are indicated in Table 



