Enzymes: How Cells Promote Chemical Activities - 105 



ENZYME (E) 



E-S COMPOUND 



(ACTIVATED) 



CATALYTIC f 

 SITE OR } 

 AREA 



ENZYME PRODUCTS 



(P 1 +P 2 ) 



E-S^— 



+ 



+ ,- 



E + S 



P r , 2 



(Pi-P,) ^~ 



■*- E-S 



* 



E + Pi + P 2 



PRODUCTS 



E. LEVEL OF ES 



* 



ENERGY 

 LEVEL 



STAGES OF REACTION 



Fig. 5-2. The mechanisms of enzyme catalysis: (1) Formation of an enzyme-substrate compound. This requires a 

 "molecular fit" between the enzyme and the substrate. (2) Energy, generated by union of E and S, activates 

 the substrate. Activation weakens certain specific bonds. (3) Splitting of substrate molecule into end products. 

 This generates the reaction energy. 



enzyme catalysis. At this time, moreover, 

 Michaelis formulated mathematical methods 

 by which this hypothesis could be tested. 

 Subsequently this brilliant theoretical analy- 

 sis was borne out by many studies. These have 

 shown conclusively that the speed of catalysis 

 varies in predictable fashion when the con- 

 centrations of (1) the enzyme, or (2) the sub- 

 strate, or (3) certain specific inhibiting sub- 



stances (p. 106) are subjected to experimental 

 variation. 



Enzyme-substrate compounds are extremely 

 unstable and short-lived, however. Conse- 

 quently they are difficult to isolate. But some 

 of them possess distinctive colors, and these 

 can be identified when a tissue is examined 

 with a spectroscope. Thus in 1943, Kurt G. 

 Stern, working at Yale University, was able 



