IV. BIOCHEMICAL SYSTEMS 237 



aniinasc,"' ^* and pyridoxal phosphate proved to l>e the coenzyme.^'' • ^''■" 



1. CJlutamic to pyruvate 



2. Glutamic to oxalacetic 



3. a-Ketoglutaratc to:"-'' •"* 



Glycine Citrulline 



Serine Oruitliine"" 



Threonine Arginine 



Cystine Lysine 



Cjsteiue Leucine 



Methionine Isoleucine 



Valine Phenylalanine 



Proline Tyrosine 



Ilistidine Tryptophan 



Chemical transaminations between pyridoxal and most amino acids^* 

 have been projected to explain the mechanism of enzymatic transamina- 

 tionJ^ It has now been shown^" that animal transaminase is activated by 

 crj'stalline pyridoxamine phosphate. This compomid requires a long incu- 

 bation period with the apoenzyme but does not appear to be converted 

 into pyridoxal phosphate either during this period or during active trans- 

 amination itself, which seems to be a necessary prerequisite for the "shuttle" 

 theories proposed^^ and which fact, therefore, renders them quite unlikely. 

 There seems to be little question but that pyridoxal phosphate is concerned 

 in most reactions of amino acids, but its mechanism of action in these proc- 

 esses is not yet clear. Pyridoxal phosphate has been sho\\Ti to be the coen- 

 zyme of some further transaminases,**^ the enzj^me synthesizing cystathio- 

 nine,*- that cleaving it to cysteine and a-ketobutyrate,*^ the serine and 



" J. H. Quastel and R. Witty, Nature 167, 556 (1951). 



6^ F. Schlenk and E. E. Snell, /. Biol. Chem. 157, 425 (1945). 



" S. R. Ames, P. S. Sarma, and C. A. Elvehjem, /. Biol. Chem. 167, 135 (1947). 



«9 H. C. Lichstein, I. C. Gunsalus, and W. W. Umbreit, J. Biol. Chem. 161, 311 

 (1945). 



'" A. E. Braunstein and M. G. Kritzmann, Nature 158, 102 (1946). 



" E. F. Gale and H. M. R. Tomlinson, Nature 158, 105 (1946). 

 \ " M. Kritzmann and O. Samarina, Nature 158, 109 (1946). 

 ! " F. Schlenk and A. Fisher, Arch. Biochem. 8, 337 (1945). 

 ' " F. Schlenk and A. Fisher, Arch. Biochem. 12, 69 (1947). 



" D. E. O'Kane and I. C. Gunsalus, J. Biol. Chem. 170, 425 (1947). 



" D. E. O'Kane and I. C. Gunsalus, /. Biol. Chem. 170, 433 (1947). 



" W. W. Umbreit, D. J. O'Kane, and I. C. Gunsalus, J. Biol. Chem. 176, 629 (1948). 



" D. E. Metzler and E. E. Snell, J. Am. Chem. Soc. 74, 979 (1952). 



" E. E. Snell, 2nd Intern. Congr. Biochem., (Paris), pp. 47-63 (1952). 



8" A. Meister, H. A. Sober, and E. A. Peterson, J. A7n. Chem. Soc. 74, 2385 (1952). 



" E. V. Rosvvell, Nature 168, 104 (1951). 



»* F. Binkley, G. M. Christensen, and W. N. Sensen, ./. Biol. Chem. 194, 109 (1952). 



