24 METABOLIC PATHWAYS IN MICROORGANISMS 



line for healthy growth, with glycerol as substrate. [When 

 glucose is the carbon source, serine may be omitted (45).] 

 The earlier report (44) listed valine as an essential growth 

 substance, but we have found it to be formed from acetolac- 

 tate, probably similarly to the formation of this amino acid 

 in yeast (46). When isotopic glucose is administered, the 

 label appears first (among amino acids) in aspartate and 

 glutamate; the same is true of administered C^^Oo. Also 

 (although this may not be related) despite the fact that 

 acetate is not oxidized by A. suhoxydans, CHgCi^OOH can 

 nonetheless give rise to labeled succinate. 



At one point we had surmised that the isocitrase reaction 

 (Fig. 1.5) (47) might be operative in A. suboxydans, and 

 that it might aid in isocitrate formation by acting in reverse 

 to form isocitrate from glyoxylate -f succinate, or even to 

 form oxalsuccinate from glyoxylate -|- malate. However, 

 although one successful experiment (48) was performed that 

 tended to support this idea, subsequent efforts have failed. 

 What has been found instead is that glyoxylate has only 



OH 



H— c— cr^ 

 c-cf 



OH 



H— C— C^ 

 I ^OH 

 H 



Fig. 1.5. The isocitrase reaction. 



