VI. BIOGENESIS 445 



amount of (liiamine pyrophosphate than the pyruvic oxidase. Here they 

 found still more cogent evidence bearing on the non-identity of the pyruvic 

 acid and the a-ketoglutaric oxidase from summation experiments. For ex- 

 anii^lo, with concentrations of substrates that were adequate to saturate 

 the respective enzymes, a-ketoglutaric acid was oxidized at the rate of 

 59 mm.* of O2 per 30 minutes, whereas the rate for pyruvic acid was 37 

 mm.' in the same period. The rate with both substrates together was 92 

 mm.', which represents a virtual summation of the two rates. Were a single 

 enzyme involved, the rate in the presence of both substrates would be ex- 

 pected to l)e in between the two rates, but never greater than the rate of 

 either. 



VI. Biogenesis 



B. C. P. JANSEN 



The biogenesis of the active part of the thiamine enzymes comprises 

 three stages: 



1. The synthesis of thiamine itself. 



2. The synthesis of the pyrophosphate of thiamine, the cocarboxylase. 



3. The synthesis of the whole enzyme, the carboxylase. 



For the second and third stages see Section IV A. In this section we shall 

 discuss only the first stage. 



Thiamine is synthesized l)y plants and also by a number of microorgan- 

 isms. Usually it is assumed that no thiamine is synthesized by animal tis- 

 sues. However, E. Abderhalden and R. Abderhalden' demonstrated that 

 animal tissues were capable of synthesizing thiamine from a solution con- 

 taining both the pyrimidine and the thiazole moieties. But this was true 

 only to a slight extent for about 1 % of the theoretical amount w^as formed 

 (see page 409). R. Abderhalden- protected rats and pigeons on a thiamine- 

 free diet from deficiency symptoms by giving the animals large ciuantities 

 of the pyrimidine and the thiazole moieties. Therefore it seems that animal 

 tissues have a trifling capacity to couple the pyrimidine and thiazole parts 

 into thiamine. 



In plants the thiamine generally is abundant in seeds and often in green 

 leaves and in roots. 



As there is a close connection l)etween microorganisms, particularly 

 mycorhizal fungi, and many plants (and often microorganisms are essential 

 for ])lants), it is difficult to state which organisms are the most important 



' K. Al.dorhMldoii niui I{. Alxlorhaklpii, I'Jlugers Arch. gcs. Phi/siol. 243, 85 (19.39). 

 2 R. Al)derhaklcn, Pflilgcrs Arch. qes. Phi/siuL 243, 762 (1940). 



