THE VITAMIN B, GROUP 665 



tion inhibits only to the extent of 12 per cent. 72 This indicates a very 

 slow rate of dissociation of the enzyme and that considerable time would 

 be required for attainment of equilibrium. This slow rate of attainment 

 of equilibrium has been advanced as the explanation for the more pro- 

 nounced effect of desoxypyridoxine in animals on a vitamin B 6 -deficient 

 diet. 72 



2,4,5-Trimethyl-3-hydroxypyridme, a bisdesoxy pyridoxine, is toxic 

 for Ceratostomclla ulmi with an inhibition index of 830-250, 25 and is also 

 toxic for excised tomato roots. 24 



2-Methyl-3-hydroxy-4-alkoxy-5-hydroxymethylpyridines. Tests with chicks 

 by methods analogous to those used for desoxypyridoxine indicate that 

 2-methyl-3-hydroxy-4-methoxymethyl-5-hydroxymethylpyridine is al- 

 most as effective as desoxypyridoxine in preventing the utilization of 

 pyridoxine. Approximately 4 molecules of the methoxy analogue 

 counteracts the response of 1 molecule of pyridoxine. Although both 

 desoxypyridoxine and the methoxy analogue act similarly in many 

 respects, the effects of otherwise lethal doses of desoxypyridoxine are 

 easily counteracted, even after a considerable period of time, by admin- 

 istration of pyridoxine; however, pyridoxine administered subsequent to 

 the methoxy analogue was generally ineffective in preventing death of 

 chicks. Thus, if the modes of action of the two compounds are similar 

 to the extent that the phosphorylated derivatives are the active inhibitory 

 forms, the rate of dissociation of the complex of the phosphate of the 

 methoxy analogue with appropriate apoenzymes would be expected to 

 be similar to the slow rate observed with pyridoxal phosphate. 



Hypoplasia, or failure of development of lymphoid elements, was the 

 outstanding feature in the spleens of chicks receiving the methoxy 

 analogue. 69 Daily feeding of 1 mg per kg of the methoxy compound to 

 puppies on a vitamin B G -deficient diet resulted in death after 1 to 4 

 weeks. One pup, however, on this dosage remained alive for a month 

 and maintained blood values only slightly lower than those of the animals 

 receiving pyridoxine, indicating some activity of the analogue in replac- 

 ing pyridoxine for this animal. 00 



When the 4-methoxy analogue of pyridoxine and tryptophan was 

 administered to rats deficient in vitamin B r „ the animals excreted less 

 xanthurenic acid and kynurenine than the animals receiving tryptophan 

 alone. 74 However, in normal animals, the analogue tended to increase 

 the amounts of these products excreted. This indicates that the analogue 

 may inhibit the action of pyridoxine to some extent; however, the in- 

 creased excretion of pyridoxic acid on administration of the analogue 

 indicated that it is cleaved and presumably utilized to some extent. 74 



