INTERCONVERSION OF SUGARS 



enzyme would also be changed. In molds it is likely that there 

 are abundant acetylglucosamine derivatives because the cell wall 

 is made up of the j3-acetylglucosamine polymer, chitin. These 

 derivatives might change the specificity of the enzyme phospho- 

 glucomutase, which in other organisms deals mainly with glucose 

 esters. And if we extend this line of thinking, we can suppose 

 that when an organism is first confronted with a new substrate, 

 it first makes use of the enzymic equipment already available. 

 Thus, an organism which normally deals with glucose could utilize 

 glucosamine by taking advantage of existing enzyme systems. 

 It would phosphorylate it with hexokinase, acetylate it with 

 coenzyme A, change the position of the phosphate group with 

 phosphoglucomutase, etc. The enzymes formed in the new 

 environment might become more efficient. Eventually, if the 

 organism previously made cellulose, it might now make chitin, 

 since the two polymers differ only in the acetyl amino group re- 

 placing a hydroxyl. 



It is futile to discuss here the possible mechanism of such an 

 imaginary process, but it may be remarked that some sort of 

 adaptation can occur which is independent of the genetic equip- 

 ment of the cells. A proof is the fact that within the same organ- 

 ism there are cells which contain different enzymes and have 

 different metabolic patterns, as, for instance, liver, brain, and 

 muscle cells. 



Ketoses from Aldoses (74) 



Lohmann in 1933 discovered an enzyme in muscle which 

 catalyzes the interconversion of glucose-6-phosphate into fruc- 

 tose-6-phosphate. Since then, several other enzymes of this 

 type have been found. One catalyzes the transformation of 

 ribose-5-phosphate into ribulose-5-phosphate, and another con- 

 verts 3-glyceraldehyde phosphate into dihydroxyacetone phos- 

 phate. Changes of a similar type have been found to take place 

 in some nonphosphorylated sugars. Thus, bacterial enzymes 

 have been prepared which transform D-ribose into D-arabinose, 



589 



