Primary Actions 285 



Enzymes, like other macromolecules, possess specificity; therefore we 

 must examine the possibiUty that genes function only in specificity- 

 conferring steps in enzyme formation. While there is no evidence that 

 mutation results in a change of enzyme specificity, there is evidence to 

 the contrary. These facts indicate that genie control may be exercised 

 at some point of enzyme formation other than in specificity-conferring 

 steps. I quote now from Bonner: "As mentioned earlier, substrate, both 

 normal and heterologous, has a profound effect upon the rate of enzyme 

 formation . . . Genetic alterations are known to affect this response 

 to substrate, and thus to determine rate of formation and concentration 

 of enzyme. The timing of appearance of enzyme is affected by sub- 

 strate and is also subject to genetic alteration. Thus one might ad- 

 vance the view, that in formation of enzyme specificity there is no 

 direct genetic control. . . . Genetic control may enter, however, in 

 determining the time and rate of enzyme formation. How genes act 

 in determining time and rate of enzyme formation is as much an 

 enigma as how genes act in determining enzyme specificity. 



"A concept of gene action involving time and rate factors fits 

 the data of microbial genetics at the present time far better than does 

 a concept involving specificity . . ." 



These conclusions of a biochemical geneticist, who obviously 

 overlooked the literature on physiological genetics prior to the time 

 of so-called biochemical genetics, are the same which I drew ( 1920a, 

 1927) from purely genetical analysis. Of course at that time we did 

 not yet deal with enzyme systems as known today, and I had 

 included specific enzymes in the more general group of active sub- 

 stances, for which I used the more inclusive term "hormones," per- 

 haps unwisely, for even at that time the term was criticized by 

 J. Huxley. But in a general way I may call the quoted sentences a 

 return to the essence of my old "physiological theory of heredity." 

 This reminds me of a review of my later more comprehensive book 

 (1938) by J. B. S. Haldane, who pointed out that all that work on 

 rate genes and attuned reaction velocities is very interesting, but that 

 the real thing is (what at that time had not been baptized thus) 

 biochemical genetics, which relates the genes to actual substances. 

 A long time has elapsed since, and biochemical genetics has had its 

 triumphant run, and brilliant discoveries of a biochemical nature have 

 been made. But when it comes to the understanding of genie action, 

 an incisive analysis such as that of Bonner leads back to the long- 

 forgotten theories of the 'twenties. I may be excused for deriving some 

 satisfaction from this. 



