52 METABOLIC PATHWAYS IN MICROORGANISMS 



time-course experiment, strongly suggests drainage of carbon 

 skeletons from the cycle. 



4. The fourth example is given by B. subtilis, which ap- 

 pears to utilize a combination of pathways, much as yeast 

 does. It is reproduced here because (a) the glycolysis pat- 

 tern is less pronounced than in yeast, and {b) the data 

 permit a testing of one of the main implications of the paper 

 of Katz and Wood, namely that carbon atoms traversing the 

 pentose cycle seemingly do so until oxidized, without escape 

 of triose units. 



One can readily recognize two distinct phases of glucose 

 oxidation in B. suhtilis (Fig. 2.8/)), as in yeast, with the 

 division occurring approximately at 1 RTU. At first, 

 glycolysis is clearly indicated by the high recovery of glu- 

 cose-C-3 and -4 in CO2. Meanwhile, the presence of an 

 alternate pathway is recognized, since the yields of Ci^02 

 from these carbon atoms are not equal, nor are they equal 

 between C-1 and C-6. The excess yield of C-1 over C-6 

 points to phosphogluconate cleavage as the alternate route 

 involved. The fact that C-2 oxidation was less than C-1 

 again suggests that some pentose phosphate was assimilated 

 —a conclusion to be expected since some cell proliferation 

 took place in this experiment. 



After exhaustion of the administered glucose in Fig. 2.8£) 

 there is a resumption of oxidation of carbons 2 and 6, and 

 to some extent carbon 1. The order of release of these car- 

 bons into COo (C-2 ^ C-6 > C-1 > C-3,4) reflects the opera- 

 tion of the TCA cycle. 



The usefulness of the radiorespirometric experiments is 

 revealed from the experiments in Fig, 2.9 on the utilization 

 of gluconate by B. suhtilis. Gluconate presumably cannot 

 be converted directly back to glucose; its oxidation would 

 seem to be obligatory by the pentose cycle, at least as far 



