676 



THE BIOCHEMISTRY OF B VITAMINS 



per day, restricts the growth of riboflavin-deficient rats to a much greater 

 extent than does the deficiency of the vitamin alone. 51 This intake of 

 isoriboflavin almost completely inhibits the growth-promoting effect of 

 10 y per day of riboflavin, but the inhibitory effect can be prevented 

 entirely by the daily administration of 40 y of the vitamin. 51 



Isoriboflavin even at concentrations 100,000 times that of riboflavin 

 does not inhibit the growth of Lactobacillus casei; and negligible activity 



OH OH OH 



I I I 

 CH 2 C C C CH 2 OH 



I I I 



H H H 



CH 3 - J 



isoriboflavin [5,6-dimethyl-9-(D,l'-ribityl)isoalloxazine] 



(less than 0.5 per cent) is obtained in attempts to replace the requirement 

 for riboflavin, with either isoriboflavin or its tetra-acetyl derivative. 57 

 However, isoriboflavin markedly stimulates the acid production and 

 growth of Lactobacillus casei in the presence of suboptimal levels of 

 riboflavin or flavin-adenine-dinucleotide. 31 



D-Araboflavin [6,7-Dimethyl-9-(D,l'-arabityl)isoalloxazine]. Administra- 

 tion of D-araboflavin (200 y per day) to rats on a riboflavin-deficient 

 diet retards growth and increases the mortality rate beyond that which 



CH 2 - 



H OH OH 



I I ! 



-C C C CH 2 OH 



I I I 



OH H H 



N 



CH 3 

 CH 3 



C=0 



I 

 ,NH 



D-araboflavin [6 ,7-dimethyl-9- (D,l '-arabityl) isoalloxazine] 



could be attributed to deficiency of the vitamin alone. 22 Only one out of 

 ten rats survives by the third week. The analogue (200 y per day) also 

 decreases the rate of growth of rats receiving low amounts of riboflavin 

 (10 y per day) to such an extent that no growth takes place by the third 



