V. SPECIFICITY OF ACTION 443 



'I'liiainiiic tiipliosphalo aiul tliiainiiio i)olypliosphate.s have an activity 

 somewhat similar to that of thiamine pyrophosphate, but they rjiianti- 

 tati\'ely are much less active; tlieir cocai'hoxyiase activity amounts to onh' 

 30% of that oi thiamine i)yrophosphate.''' ^ 



Velluz ct al? tried to restore the carboxylatic activity of apocarboxylase, 

 obtained l)y washing yeast with an alkaline phosphate sokition. From 

 four to li\'e times more thiamine triphosphoric acid than thiamine pyro- 

 phosphate was required to saturate the \vashed yeast. The resynthesized 

 enzymatic system developed 80% of the activity of the one rebuilt with 

 thiamine pyrophosphate. 



Plotka et al.^ studied the action of thiamine triphosphoric acid on the 

 heart. On the excised frog's heart thiamine triphosphoric acid exerts a 

 slight positive inotropic action on the normal organ and restores the regu- 

 larity of the fatigued heart. On the rabbit's heart in situ, thiamine triphos- 

 phoric acid protects the organ against fibrillation induced })y faradization. 

 Thiamine pyrophosphate also exhibits some antifibrillatory properties but 

 much less than thiamine triphosphoric acid. Plotka et al. in the same article 

 discussed the problem of the existence of thiamine triphosphoric acid in organ- 

 isms, and they think it is justifiable to consider that thiamine triphosphoric 

 acid plays a role in the special metabolism related to nerve impulse trans- 

 mis.sion. 



C. SUBSTRATE SPECIFICITY 



Green et al? studied the activity of a purified carboxylase from yeast on 

 different substrates (Table III). 



Thus the a-ketonic acids, in addition to pyruvic acid, are decarboxylated 

 also, but the higher homologs are attacked at a lower rate. 



The specificity of carboxylases from animal tissues was somewhat differ- 

 ent (Green et al.^). These preparations had no action on oxalacetic acid, 

 mesoxalic acid, a-ketocaproic acid, or phenylpyruvic acid. They decarboxy- 

 lated a-ketobutyric acid under formation of propioin, according to the equa- 

 tion 



2CH3CH2COCOOH -> CH3CH.2CHOHCOCH2CH3 + 2CO2 



and a-ketoglutaric acid to succinic semialdehyde and CO2: 



COOHCHa-CHiCOCOOH -> COOHCH2CH2CHO -|- CO2 



5 M. Herbain, Bull. soc. chim. biol. 32, 784 (1950). 



« H. Rou.x and A. Callandre, Bull. soc. chim. biol. 32, 793 (1950). 



' L. Velluz, G. Amiard, and J. Bartos, /. Biol. Chem. 180, 1137 (1949). 



8C. Plotka, M. Peterfalvi, R. Jequier, and L. Velluz, Am. J. Physiol. 158, 279 



(1949). 

 9 D. E. Green, W. Westerfeld, B. Venneslund, and W. E. Knox, ./. Biol. Chem. 145, 



69 (1942). 



