IV, BIOCHEMICAL SYSTEMS 437 



CUSO4 , or HgCNOs) gave complete inhibition, but .U/10,000 ZnSO^ showed 

 no inhibition at all. 



Several other inhibitors are described lor carboxylases. Cajori"^ found 

 inhibition for carboxylase from yeast by hemin; the enzyme was activated 

 by cysteine. Kensler cl al}^ showed inhibition of yeast carboxylase by the 

 split products of N,N-dimethylaminobenzene; they conhrmed the stimu- 

 lation by cysteine. 



Stumpf," working with a pja'uvic oxidase from Proteus vulgaris, found 

 that inorganic pyrophosphate in 3.4 X 10~* M concentration inhibits the 

 enzyme activity; this inhibition is reversed by 0.7 X 10~^ M thiamine pyro- 

 phosphate. He ascribed this inhibition by inorganic pyrophosphate to its 

 reversible union with the magnesium-protein complex, thus blocking a simi- 

 lar union with thiamine pyrophosphate. Carboxylase activators were dem- 

 onstrated by Greenberg and Rinehard.^'- They found that cysteine, NaHSOs, 

 and phenylhydrazine were able to activate the thiamine pyrophosphate 

 enzj-mes. Tauber'^* found that sodium cyanide is a good activator. All these 

 compounds combine with aldehyde and ketone groups. 



B. COENZYIMES 



Until recently only one thiamine-containing coenzyme was known, i.e., 

 thiamine pyrophosphate. Thiamine itself and thiamine monophosphate are 

 without any coenzyme activity. 



Several years ago, some French authors"* prepared thiamine triphosphate 

 and thiamine polyphosphates. 



In thiamine pyrophosphate the pyrophosphoric acid is attached to the 

 thiazole group of the thiamine molecule. Thus the formula of pyrophosphate 

 is 



N— CH Cl CH3 



II II II 



CH3— C C— CH2— N— C O O 



II \ II II 



N=C C— CH2— CH2O— P— O— P— OH 



\ / II 



H2N HC— S OH OH 



Roux et al. assumed that in thiamine triphosphate the third phosphate 

 group is attached to the NH2 of the pyrimidine. Thus it has the following 

 formula. 



" D. M. Greenljerg and J. F. Rinehart, Froc. Soc. Exptl. Biol. Med. 43, 495 (1940). 

 " H. Tauhcr, The Chemistry of Enzymes, p. 250. John Wiley and Sons, New York, 



1950. 

 "» H. Roux, Y. Feysseire, and G. Duchesne, Bull. soc. chiin. biol. 30, 592 (1948). 



