V. SPECIFICITY OF ACTION 



353 



adjacent c?5-hydroxyl groups, as in w^o-inositol, are essential for activity. 

 The activity for some organisms of scyllitol and mytilitol (C-methylscyl- 

 litol), which have no czs-hydroxyl groups, and L-inositol, which has two 

 pairs of c/s-hydroxyl groups, one on each side of the ring, indicates that the 

 three adjacent cfs-hydroxyls are not always essential. 



A different kind of specificity is suggested by the work of Magasanik 

 and Chargaff^^ on the oxidation of inositol isomers by Acdobacter suboxy- 

 dans. This organism, which can oxidize inositol to a cyclic ketone, shows a 



Fig. 2.11 



TABLE V 



Oxidation of Inositol by Acetobacter suboxydans 



very interesting enzyme specificity for inositol isomers. In the isomers 

 which were oxidized by this organism, either one or two hydroxyl groups 

 in the molecule were oxidized depending upon the inositol isomer tested. 

 To explain this specificity Magasanik and Chargaff'^ made two assump- 

 tions: first, that the inositols exist chiefly in the "chair" form, as cyclo- 

 hexane does; and, second, that the most stable configuration of an inositol 

 molecule has the maximum possible number of hydroxyl groups in the 

 efiuatorial plane (positions marked "Eq." in Fig. 2) and the minimum num- 

 ber of hj'droxyl groups in the pole regions (positions marked "N" and "S" 

 in Fig. 2). The results of these experiments are summarized in Table V." 



11 B. Magasanik and E. Chargaff, J. Biol. Chem. 174, 173 (1948). 



