184 THE BIOCHEMISTRY OF B VITAMINS 



cleave tryptophan to form serine and a second would catalyze the deamin- 

 ation of serine, yielding the observed products, ammonia and pyruvic 

 acid, was ruled out when it was shown that the preparation cannot 

 catalyze the deamination of serine. 



An independent investigation has been carried out upon the enzymatic 

 degradation of tryptophan by cellular extracts from this same organ- 

 ism. 200 In this study, the biological preparations used had apparently not 

 been adequately resolved into individual enzyme systems, since the pro- 

 duction of indole and tryptophan was accelerated by each of four sub- 

 stances: a nicotinic acid coenzyme, free riboflavin, pyridoxal phosphate, 

 and a porphyrin-containing enzyme (verdoperoxidase) . A maximum rate 

 of reaction was achieved only when all four of the stimulating factors 

 were added. By chromatographic analysis it was shown that alanine was 

 formed during the "reaction." It could, however, have been formed 

 secondarily from pyruvic acid following the initial cleavage. Were alanine 

 a primary product of the reaction, it would mean that the cleavage is a 

 reductive one, and the reaction would of necessity have to be coupled 

 with a second reaction in which hydrogen atoms are made available. The 

 effect of the hydrogen-transporting agents upon the rate of indole forma- 

 tion probably is the result of the oxidative removal of the other products 

 of the primary reaction. 



Relationship of Vitamin B G and Amino Acid Requirements in Bacterial 

 Metabolism. The determination of the amino acid requirements of sev- 

 eral bacteria has indicated processes in amino acid syntheses, other than 

 those completely characterized, for which the vitamin B 6 coenzyme is 

 undoubtedly essential. In most instances, the variations in amino acid 

 requirements resulting from the addition of pyridoxal or pyridoxamine 

 can be explained by assuming catalysis of reactions of the types which 

 have been demonstrated in cell-free systems. 



It has been observed that the presence of three amino acids in particular 

 — lysine, threonine and alanine — radically affects the pyridoxal or pyri- 

 doxamine requirement of certain bacteria. 227, 228, 229 In the absence of 

 these amino acids the vitamin B 6 requirement of these organisms may be 

 more than ten times that when they are present. It was observed that 

 these amino acids were no longer essential when pyridoxine was replaced 

 by pyridoxal or pyridoxamine in the media of certain bacteria. The effect 

 presumably did not occur as the result of an independent function of 

 pyridoxine, but rather reflected an inadequate chemical conversion of the 

 inactive pyridoxine during autoclaving; hence, the organisms were not 

 supplied sufficient amounts of active precursors of the vitamin B 6 coen- 

 zyme to carry out the synthesis of these three amino acids. Formation 

 of these acids was independent of the carbon dioxide tension, and it is 



