208 



Peter D. Klein 



WiNZLER (3). H{B) was defined as the logarithm of the total number of 

 compounds tested, both for ability to replace the natural co-factor and for 

 those having antimetabolite activity. H(B.A) was calculated from the com- 

 pounds active as antimetabolites plus those having substrate activity; in the 

 former case, the inhibition index (number of molecules of inhibitor required to 

 overcome the action of one molecule of the true compound) was considered as 

 the reciprocal of biological activity and suitably transformed to agree in dimen- 

 sion with the other data. H(B.A.S) was, of course, derived from the group 

 which showed ability to replace the natural co-factor. 



RESULTS AND DISCUSSION 



The H functions and AHi*, Ai/u* and ^Hju* are fisted for a variety of 

 compounds in Table 1. In addition, compounds for which partial data were 



Table I 



Compound 



Organism 



N H{B) H{B.A) H(B.A.S) A/Zj* AHu* AZ/fn 



Key: MO: Micro-organism 

 R: Rat 

 C: Chick 



F: Frog 



G: Guinea pig 



D: Dog 



available are included. Fig. 3 presents some values for the first group in graphic 

 form. 



It can be seen that there is a range in H{B.A) of 1.39 to 4.90 and in H(B.A.S) 

 of 0.13 to 3.88. There is also a marked tendency for A/Zn* to be smaller than 

 A//^*, suggesting that the greater portion of the selection process is assumed by 

 the apo-enzyme/co-enzyme complex formation, but sight must not be lost of 



