206 Peter D. Klein 



The collision of the holo-enzyme with a potential substrate represents another 

 decision point (Decision Point 2). Again, a complex will be formed if sufficient 

 information is transferred. It is at this point that the pseudo-holo-enzyme 

 must present the wrong information in order to be an effective inhibitor. This 

 results in repeated cychng in the innermost loop diagrammed. 



The enzyme-substrate complex has a finite probability, designated Probabi- 

 Hty Point 3, of decomposing unchanged before the reaction is catalysed to 

 decompose the substrate into product and regenerate the holo-enzyme. 



There are, then, two points in tliis flow sheet at which information can be 

 exchanged; between the co-factor and the apo-enzyme and between the holo- 

 enzyme and the substrate. These are the two points to which attention will be 

 devoted. 



At neither decision point is the decision unequivocal. There are several 

 types of co-factor-substances which may form a complex with the apo-enzyme 

 and several of these complexes are acceptable, though to differing degrees, to 

 the substrate. The situation is graphically presented in the set diagram Fig. 2. 

 The largest circle represents the class of all possible organic compounds. Let 

 B designate these substances. A subset of 5, composed of the organic substances 

 which normally occur in cells, is designated C. Another subset of B, designated 

 A, is comprised of substances acceptable to the apo-enzyme for complex forma- 

 tion. The set A.C'\ includes those compounds normally occurring in cells which 

 are able to complex with the particular apo-enzyme considered ; the set (A~A.C) 

 contains those substances which form a complex with the apo-enzyme but are 

 not normally found in the cell. 



A subset of A, designated A.S, contains all compounds which complex with 

 A and react with the substrate. (There may be other substances in B which 

 would react with the substrate, if complexed with a proper apo-enzyme ; but 

 these are not of concern here.) These substances which are contained in the 

 set C.A.S are the natural co-factors for the apo-enzyme-substrate pair under 

 consideration; the substances in the set A.S-C.A.S are artificial co-factors; 

 the substances C.A-C.A.S are natural antimetabohtes ; those in the set A-A.S 

 are artificial antimetabolites. 



The information measures associated with the two decision processes can 

 be derived from the diagram. Let H(X) designate the uncertainty associated 

 with the set X; then: 



H(C) is the uncertainty of substances in a normal cell. To give this quantity 

 meaning, we shall consider it to be the uncertainty about the nature of an 

 organic molecule which normally collides with the apo-enzyme. 

 H{C.A) is the uncertainty concerning a substance which has formed a 

 complex with the apo-enzyme. 



H(C.A.S) is the uncertainty concerning the complex which has reacted 

 with the substrate. It should be noted that in dealing with a given apo- 

 enzyme and a given substrate (or class of substrates) all uncertainties in 

 question are due to the co-factor. 



t The set X. Y contains all substances which belong to both the set X and the set Y. The 

 set JV- 7 contains those substances which are contained in A' but not in Y; alternatively this set 

 is designated X-X. Y, all substances which belong to X but not to both X and Y. The latter 

 notation is more explicit and will be used here. 



