192 Essays in Biochemistry 



apparently used for the biosynthesis of protein from small precursors, 

 since the ability of glucose-grown amino acid-deficient mutants of this 

 organism to attack ?m/o-inositol was stimulated by the amino acid 

 required for growth. 15 These experiments indicated that the attack 

 on the cyclitols was mediated by adaptive enzymes whose synthesis 

 could be induced by myoinositol. The validity of this assumption 

 was confirmed by the demonstration that extracts of m?/o-inositol- 

 grown cells possessed two enzymes (later identified as a dehydrogenase 

 acting on inositols II and IV and a dehydrase acting on the ketoinosi- 

 tols X and XIV), which were not found in extracts of glucose-grown 

 cells. 16 The enzymes could be separated by treatment with protamin 

 sulfate. The dehydrogenase was precipitated and could be redissolved 

 by the dissociation of the insoluble protamin salt with polymeth- 

 acrylate. 



The dehydrogenase purified in this fashion was found to catalyze 

 the reduction of diphosphopyridine nucleotide (DPN), but not that 

 of triphosphopyridine nucleotide, by myoinositol, and more slowly by 

 D-inositol, in the presence and absence of inorganic phosphate. The 

 equilibria of these reactions were too unfavorable for dehydrogenation 

 (even at a relatively high pH) to permit the isolation of the products; 

 therefore the reverse reaction, the oxidation of DPNH by ketoinositols, 

 was investigated. 2-Keto-myo-inositol (X) reacted with DPNH in 

 the presence of the enzyme to give equimolar amounts of DPN and of 

 ?m/o-inositol (II) (determined by bioassay with inositol-less Neuro- 

 spora crassa) ; L-l-keto-myo-inositol (XIV) reacted with DPNH to 

 give DPN but was itself not converted to myoinositol. These re- 

 sults indicated that the enzyme catalyzes the conversions of myo- 

 inositol (II) and of D-inositol (IV) to monoketones by removing the 



O 



Reaction la + DPN + , * + DPNH + H" 



Reaction 1 b + DPN + , ' + DPNH + H + 



IV XIV 



