D. E. GREEN 



tural organic chemist played the leading roles, and indeed they laid 

 the foundations for an exact science. Hence, it is hardly surprising 

 that dynamic problems such as those of intermediary metabolism were 

 approached more from the direction of what may be called chemical 

 morphology than from the point of view of physiology. Perhaps the 

 best way of illustrating the point is to recall the sensation which was 

 produced by Schoenheimer's (5) early isotope experiments. His con- 

 ception of an organism as a chemical system in a constant state of flux, 

 in dynamic as opposed to static equilibrium, bore the same relation to 

 the classical biochemical conception that the Schrodinger-Heisenberg 

 conception of the atom bears to the rigid atom of the late 19th century. 

 This is not to imply that the groundwork for Schoenheimer's concep- 

 tion was not already laid in the literature. The students of enzymes 

 have long been aware of reversible equilibrium systems; but biochem- 

 ists generally were unable to project the implications of these reversible 

 systems in terms of intermediary metabolism. The outstanding re- 

 searches of Schoenheimer and Krebs have done much to orient research 

 on intermediary metabolism along more peculiarly functional lines; 

 but, nonetheless, not more than the fringe of biochemical thinking has 

 been disturbed. Intermediary metabolism is still being taught and 

 discussed without any reference to the catalysts responsible for each of 

 the transformations. Discussing the behavior of a car without refer- 

 ence to the motor represents an analogous situation. This state of af- 

 fairs provides some reason for attempting an interpretation of biochem- 

 istry in terms of enzymes and enzymic phenomena. What follows will 

 be rather sketchy, not only because of the limitations of space, but also 

 in some cases because of the inadequacy of available information. 

 However, the purpose of this essay is more to show that enzymes pro- 

 vide a logical and rational approach to many fields of biochemistry 

 and medicine rather than to attempt a comprehensive survey of the 

 enzyme field. 



Living systems carry on their activities by virtue of myriads of 

 chemical reactions which collectively are referred to as intermediary 

 metabolism. Physiological functions such as growth, reproduction, 

 secretion, nerve conduction, muscular contraction, etc., are integra- 

 tions of whole series of chemical events in intermediary metabolism. 

 These chemical events with few exceptions are not spontaneous proc- 

 esses. They require the presence of highly specialized protein cata- 



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