194 Essays in Biochemistry 



group (reaction 2a). A similar attack converts L-1-keto-wi^o-inositol 

 to the same product at a slower rate (reaction 2b). 



The presence of the dehydrogenase and the dehydrase in extracts of 

 ra?/o-inositol-grown cells indicates that the initial attack of A. aero- 

 genes on m7/o-inositol is a dehydrogenation (reaction la), followed by 

 dehydration (reaction 2a). The ability of inositol-adapted cells to 

 attack 2-keto-wi/o-inositol is in agreement with its role as an interme- 

 diate in this reaction sequence. The simultaneous adaptation to 

 D-inositol and L-1-keto-m^o-inositol finds its explanation in the fact 

 that these compounds are attacked by the same enzymes as myo- 

 inositol and 2-keto-ra?/o-inositol and converted to a common product, 

 the enol XXIII. 



The further steps in the degradation of rat/o-inositol have as yet 

 not been demonstrated in a cell-free system. The rapid oxidation and 

 fermentation of L-l,2-diketo-m7/o-inositol (XII) by suspensions of 

 rai/o-inositol-grown cells suggests that this compound is an intermedi- 

 ate in the degradation of m?/o-inositol. It could presumably arise by 

 oxidation of the enol XXIII (reaction 3). 



Reaction 3 



XXIII 



The broad outlines of the metabolic pathway leading to the com- 

 plete degradation of ?m/o-inositol were elucidated by the study of the 

 products of inositol dissimilation under aerobic and anaerobic condi- 

 tions. 17 The oxidation of w?/o-inositol, 2-keto-ra?/o-inositol, or 1,2- 

 diketo-m?/o-inositol by resting cell suspensions of A. aerogenes yielded 

 the same products as the oxidation of glucose. The amount of C0 2 

 produced and of 2 taken up was sufficient for the complete oxidation 

 of one-half of the molecule to CO2 and H 2 0. The other half of the 

 molecule was apparently assimilated as material of the composition 

 C 3 H 6 0.3. In the presence of dinitrophenol, an agent known to inhibit 

 oxidative assimilation, the oxygen uptake approached the theoretical 

 values for complete oxidation. In the presence of As 2 3 , an inhibitor 

 of pyruvate degradation, glucose was degraded largely to 3-carbon 

 compounds (pyruvate and lactate) whereas w?/o-inositol and the keto- 

 inositols were dissimilated to a mixture of 3-carbon compounds (pyru- 

 vate and lactate), 2-carbon compounds (acetate and ethanol), and 



