Metabolism of Inositol 191 



plex may be held together by bonds between the enzyme or a metal ion 

 associated with the enzyme and the two required equatorial hydroxy! 

 groups which occupy the same plane as the hydrogen atom (Fig. 4). 



The rules which have been presented apply to hexahydroxycyclo- 

 hexanes, pentahydroxycyclohexcmes, and their keto derivatives. Tri- 

 hydroxycyclohexanes are oxidized by a different enzyme and one sub- 

 ject to rules which have as yet not been elucidated; it is possible that 

 this enzyme is identical with the one responsible fur the oxidation of 

 straight-chain polyhydroxy compounds. 



The biological significance of the inositol dehydrogenase of A. sub- 

 oxydans is not known. The enzyme is not adaptive but is present in 

 cells grown in the absence as well as the presence of inositol. The 

 organism obtains useful energy but no building blocks for the synthesis 

 of its protoplasm by the incomplete oxidation of the inositols. In other 

 species of microorganisms, however, ??it/o-inositol can be metabolized 

 with the production of energy and building blocks. This can be in- 

 ferred from the observation that seven bacterial species of a group of 

 fourteen can grow on ?ni/o-inositol as the only source of carbon. 13 One 

 of these species, Aerobacter aerogenes, was chosen for a study of this 

 extensive degradation of the inositol molecule. 



It was found that in addition to ?m/o-inositol (II), four other cycli- 

 tols [D-inositol (IV), 2-keto-?m/o-inositol (X), L-l-keto-mi/o-inositol 

 (XIV) and L-l,2-diketo-m(/o-inositol (XII) 1 could support the growth 

 of capsulated strains of A. aerogenes as sole sources of carbon. Scyl- 

 litol (I) was not attacked by the microorganism but inhibited specifi- 

 cally and reversibly the dissimilation of these five compounds. The 

 other cyclitols tested (V, VI, XIX, XX, XV, XI, XVII, and XIII) 

 showed neither growth-supporting nor inhibitory activity. 14 



Suspensions of cells grown on glucose did not oxidize the five cyclitols 

 immediately but only after a period of lag of about 1 hour, although 

 suspensions of cells grown on ra?/o-inositol oxidized this compound as 

 well as the other four cyclitols without lag. The process occurring 

 during the period of lag could be shown to require energy by its sus- 

 ceptibility to the inhibitory action of dinitrophenol. The energy was 



