Metabolism of Inositol 



193 



hydrogen atom from carbon atoms carrying a polar hydroxyl group 

 (reactions la, b). 



The Aerobacter enzyme had thus singled out the same carbon atom 

 of mt/o-inositol for dehydrogenation as the Acetobacter enzyme. Ap- 

 parently, a carbon atom carrying a polar hydroxyl group is more sus- 

 ceptible to dehydrogenation than one carrying an equatorial hydroxyl 

 group; this concept is in good agreement with the observation men- 

 tioned earlier that platinum similarly catalyzes specifically the attack 

 on the carbon atom of ?m/o-inositol which carries the polar hydroxyl 

 group. The inability of the Aerobacter enzyme to act on most of the 

 cyclitols which are attacked by the Acetobacter enzyme shows that 

 the steric requirements of the two enzymes other than their specificity 

 for polar hydroxyl groups are not the same. 



A. suboxydans does not possess the enzymes necessary to carry the 

 attack on mi/o-inositol beyond 2-keto-rayo-inositol. A. aerogenes, on 

 the other hand, possesses an enzyme found in the supernatant fluid 

 after treatment with protamin sulfate, which acts on 2-keto-myo- 

 inositol (X) in the absence of added cofactors. The strong absorption 

 band of the product {E, 4000) at 261 m^ and its reducing properties 

 suggested it to be an a, ft unsaturated ketone. This assumption was 

 confirmed by the isolation of this compound by means of phenylhydra- 

 zine. The hydrazone was identified by its reaction with periodic acid 

 and its absorption spectrum as the bisphenylhydrazone of 2,3-diketo-4- 

 deoxy-e/w-inositol (XVI) ; the same compound had previously been 

 obtained through the oxidation of L-2-deoxy-mwco-inositol (XV) by 

 A. suboxydans. These results show the enzyme to be a dehydrase 

 which converts 2-keto-mt/o-inositol to the enol XXIII by attacking 

 one of the equatorial hydroxyl groups in meta position to the keto 



Reaction 2 a 



Reaction 2 b 



XXIII 



H 



XIV 



XX 



XVI 



