58 CHEMISTRY OF PLANT LIFE 



each of the four alcoholic groups in the molecule is identical with 

 the corresponding groups in a fermentible hexose. 



Oxidation by Bacteria. The bacillus Bacterium xylinum con- 

 tains an enzyme, or enzymes, which promote the oxidation of the 

 aldehyde group of an aldose sugar to COOH, or of one alcoholic 

 CHOH group next the terminal CH^OH group of a hexatomic 

 alcohol to C = O. But these oxidizing enzymes affect only those 

 compounds in which the OH groups are on the same side of the 

 two asymmetric carbon atoms next the end of the molecule where 

 the oxidation takes place, as indicated in the following groupings. 



H C OH H C OH H C OH H C OH 



II ! I 



H C OH or H C OH but not HO C H or HO C H 



II II 



CHO CH 2 OH CH 2 OH CHO 



The configuration of the remainder of the molecule is 

 immaterial to action by these oxidizing bacteria; hence, the 

 enzymes in this case are apparently concerned only with the con- 

 figuration arrangement of a portion of the molecule, instead of 

 with the whole hexose grouping, as in the cases of the other reac- 

 tions which have been thus far considered. 



It is apparent from these illustrations, and from many more 

 which might be cited, that there is a very definite relation between 

 the molecular configuration of a carbohydrate and its biochemical 

 properties, as represented by the possibilities of the action of 

 enzymes upon it. The probable nature of this relationship will be 

 better understood after the general questions involved in the mode 

 of enzyme action have been considered (see chapter XIV). But 

 for the present, it will be sufficient to note that it seems to be 

 necessary that the enzyme shall actually fit the molecular arrange- 

 ment of the compound at all points, in the same way that a key 

 fits its appropriate lock; or a still better illustration is that of the 

 fitting of a glove to the hand. On the basis of the latter illus- 

 tration, it is just as impossible for a dextro-enzyme to affect a 

 levo-sugar, or for a-glucase to affect a /3-glucoside, as it is to fit 

 a right-hand glove upon a left hand. Further attention will be 

 given to these matters in later chapters. 



