Carbohydrates in Aromatic Compound Biosynthesis 261 



SA synthesis it gave the distribution of activities summarized in Fig. 2. 

 The value for each SA carbon atom is represented as the fraction of 

 activity of the labeled atom of the glucose from which the SA had 

 arisen. Except for S-l and S-5, the SA atoms were 80-90% accounted 

 for by large contributions from glucose atoms 1, 2, 3, 4, and 6. In 

 addition there were small incorporations which could not be deter- 

 mined accurately. The large "deficiencies" in S-l and S-5 presumably 

 arise mostly from G-5, the one carbon atom of glucose that could not 

 be tested experimentally. 



3 or 4 (0.86) 

 COOH 



2 (0.4) 

 5 (0.5) 



(0.25) 1 

 (0.60) 6 



(0.22) 2 

 (0.6) 5 



1 (0.4) 

 6 (0.5) 



2 (0.24) 



3 or 4 (0.59) 



3 or 4 (0.9) 

 Fig. 2. Major contributions of glucose carbon atoms to shikimate biosynthesis. 



It is clear that S-2 is derived almost entirely from G-l and G-6, 

 S-l from G-2 and G-5, and S-7 from G-3, 4. The G-l and G-6 con- 

 tributions are about equal, as are those from G-2 and G-5, and so it 

 may be assumed that the G-3 and G-4 contributions are also about 

 equal. From this distribution it may be concluded that S-2, 1, 7 is 

 derived from a three-carbon intermediate of glycolysis, which as 

 pointed out above cannot be pyruvate. 



The derivation of the 3, 4, 5, 6 portion of SA from glucose is more 

 complex. S-6, S-5, and S-4 are derived 0.8-0.9 from G-l, 6, G-2, 5, 

 and G-3, 4, respectively. Since the G-6/G-1 and the G-5/G-2 contri- 

 butions are both present in a ratio of about 2.5/1 it seems reasonable 

 to assume the same ratio for the G-4/G-3 contributions. S-3 arises 

 from G-3, 4 and G-2, also in a 2.5/1 ratio. Such a distribution of 

 label can be explained by assuming that S-3, 4, 5, 6 was derived from 

 tetrose phosphate whose formation had involved, as shown in Figs. 3 

 and 4, the glycolytic as well as the pentose phosphate pathway. 



In reaction 1 (Fig. 3) fructose-6-phosphate (F-6-P) (I), derived 

 directly from the glucose administered, exchanges under the influence 

 of transaldolase with triose phosphate which has been equilibrated by 

 triose isomerase. This exchange incorporates G-l, 2, 3 into the "bot- 



