FACTORS INFLUENCING B VITAMIN REQUIREMENTS 285 



forms. Thiamine also occurs in the form of the pyrophosphate (cocar- 

 boxylase), but the relative potency of this form for living things other 

 than bacteria is apparently unknown. (Certain strains of Neisseria gonor- 

 rheae even require this form for growth, and thiamine itself is not only 

 inactive, but inhibits growth, being competitively reversed in its action 

 by the pyrophosphate.) 104 Certain protozoa at least, and perhaps a few 

 higher animals, are able to use either the thiazole or the pyrimidine frac- 

 tion of thiamine for growth, 105 so that in a general sense, the presence 

 of these substances and their activity must be considered in the nutrition 

 of members of phyla below the chordates. 



A thiol form of thiamine, and its oxidized disulfide form (and their 

 pyrophosphates), are believed to exist, 106 and both thiamine and cocar- 

 boxylase disulfide have been shown to be active in the catatorulin test 

 with deficient pigeon brain (p. 51). The presence of these forms must 

 be considered, if they are found to have biological activity for any species 

 under consideration. 



Finally, Polonovski et al. 107 recently reported an interesting series of 

 studies in which a number of natural and synthetic pterins were found 

 to substitute for thiamine (or riboflavin) in pigeons and rats. Fluores- 

 cyanine (a fluorescent pigment from the scales of certain fish) was able 

 to eliminate the symptoms of deficiency in thiamine-deficient rats and 

 pigeons, and to increase the oxygen uptake and carbon dioxide evolution 

 from thiamine deficient rat brain. Injection of 50 to 100 /xg/day of a 

 number of synthetic pterins produced similar effects, and the fact that 

 oral dosage was similar in effect showed that the result was not due to 

 intestinal synthesis by microorganisms. Indeed the pterins were found to 

 be incapable of replacing thiamine for microorganisms. It was also re- 

 ported that in cecectomized rats 10S xanthopterin, isoxanthopterin, folic 

 acid, and lumazine could be substituted for thiamine, isoxanthopterin 

 being the most active. Such results, if verified, suggest the possibility 

 that the biological and structural specificity of many of the B vitamins 

 (and other nutritionally active substances) may not be as great as has 

 been generally presumed heretofore, and that the specificity may rest 

 rather in the chemical structure and groupings involved in the precise 

 functions of the vitamin. 



(2) Riboflavin 



Riboflavin is known to exist in free and combined forms and as the 

 5-phosphate, in the form of the flavin-adenine-dinucleotide, and in both 

 oxidized and reduced states (p. 32). The relative potencies and avail- 

 ability of these forms, however, for various species, are not known, though 

 it is generally assumed that riboflavin is seldom present in forms in which 



