238 



PYRIDOXINE AND RELATED COMPOUNDS 



threonine deaminases of Neurospora,^^ and a D-serine deaminase from bac- 

 teria.** 



There apparently also exists a transaminase from glutamine to a variety 

 of keto acids**^ in which the a-amino group of the glutamine is removed 

 before that of the amide. This reaction is also catalyzed by pyridoxal phos- 

 phate. 



D. RACEMASES 



Pyridoxal phosphate is the coenzyme of an enzyme catalyzing the forma- 

 tion of an equilibrium mixture of DL-alanine from either d- or L-alanine.*® 

 There are indications that a variety of such racemases may exist. 



E. TRYPTOPHAN 



In addition to decarboxylation and transamination, tryptophan is me- 

 tabolized by pyridoxal phosphate enzymes as follows: 



1 . Tryptophanase :*^ this enzyme catalyses the breakdown of tryptophan 

 to indole, pyruvate, and ammonia. 



Indole 



+ 

 serine 



Tryptophan 



Kynurenine 



Indole + pyruvate -t- ammonia (bacteria) 



Kj'nurenic acid 



3-Hydroxykynurenine 



Xantluiicnic acid 



Anthranilic 

 acid + alanine 



3-Hydroxyanthranilic acid 



/ \ , . 



Quinolinic acid Nicotinic acid 



Tryptophan Metabolism 



2. In the animal, tryptophan is metabolized through kynurenine accord- 

 ing to the accompanying scheme. Pyridoxal phosphate is the coenzyme of 

 the reaction converting kynurenine to anthranilic acid and alanine**- *^ and 



*^ J. L. Reissig, Arch. Biochevi. and Biophys. 36, 23-4 (1952). 



8* D. E. Metzler and E. E. Snell, J. Biol. Chem. 198, 363 (1952). 



86 A. Meister and S. V. Tice, /. Biol. Chem. 187, 173 (1951). 



86 W. A. Wood and I. C. Gunsalus, J. Biol. Chem. 190, 403 (1951). 



87 W. A. Wood, I. C. Gunsalus, and W. W. Umbreit, /. Biol. Chem. 170, 313 (1947). 



88 A. E. BraushteTn, E. V. Goryachenkova, and T. S. Paskhina, Biokhimiya 14, 163 j 

 (1949) [C. A. 43, 6264 (1949)]. 



89 C. E. Dalgliesh, W. E. Knox, and A. Neuberger, Nature 168, 20 (1951). 



