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F 
  
 	1. Enzyme does not affect ΔG or ΔGo between S and P (i.e., equilibrium) 
 	2. Enzyme reduces Ea : Ea (catalyzed) Ea (uncatalyzed) 
  
 	A more complete way of showing the effects of enzymes :  
  
 	Enzymes bind to 
 	substrates, so 
 	G (ES) G (E S) . 
  
 	However, if all they 
 	did was to bind, then Ea 
 	=ΔG (ES) for the reaction 
 	would not be reduced. 
  
 	So when they bind the 
 	substrate, they stress 
 	It in some way, raising 
 	G (ES) for part of the 
 	substrate and reducing 
 	ΔG (ES) (=Ea) . 
  
 	Quantitatively, what is the effect of reducing Ea -  
  
 	For reaction A	B, V = k A  
  
 	k = (T/h) exp (-Ea/RT) 
 	= Boltzman's constant; h = Plank's constant, 
  
 	So k and thus V are inversely and exponentially 
 	related to Ea and directly related to T :  
  
 	A 6 kJ/mol reduction in Ea gives ca 10x increase in k 
 	and V 
 	k ~ exp (+6000/8.3 300) ~ 11 
 	 (reduction in Ea is an increase from -Ea) 
  
 	V (catalyzed) /V (uncatalyzed) for various enzymes 
 	varies from 104 to 1021 , meaning Ea is reduced by ca 
 	23 to 126 kJ/mol 
  
 	How do enzymes reduce Ea -  
  
 	These effects raise G (ES) : cage effect, orientation, 
 	steric straining of bonds (stress from H-, 
 	Vanderwaal's, ionic bonds) , dislocation of bonding 
 	electrons through +/- charges 
  
 	These effects reduce G (ES) : covalent bonds, acid- 
 	base catalysis, low-barrier hydrogen bonds, and metal 
 	ion catalysis 
  
 	Different classes of enzymes may use different 
 	mechanisms :  
  
 	1. Oxidoreductases (oxidation-reduction reactions) 
 	2. Transferases (transfer of functional groups) 
 	3. Hydrolases (hydrolysis reactions) 
 	4. Lyases (addition to double bonds) 
 	5. Isomerases (isomerization reactions) 
 	6. Ligases (formation of bonds with ATP cleavage) 
  
 	Examples :  
  
 	Orientation, 
 	Cage effect 
  
 	Strain 
  
 	Charge effects, 
 	Covalent bonds, 
 	Acid-base catalysis 
  
 	An example 
 	of an enzyme 
 	that sterically 
 	strains the 
 	substrate :  
  
  Lysozyme Hydrolysis 
 	distorts the bonds	breaks the 
 	of one of the	polysaccharide 
 	sugars in the	chain and 
  polysaccharide weakens 
 	of a bacterial	the wall so 
 	cell wall	that the cell 
 	lyses. 
 	It also places a 
 	partial charge on 
 	the substrate, 
 	making it react 
 	more easily 
 	with water 
 	 (hydrolysis) . 
  
 	Example of an enzyme mechanism using covalent 
 	bonds, acid-base catalysis, low-barrier hydrogen 
 	bonds 
  
 	Serine protease (e.g., trypsin, chymotrypsin, 
 	acetylcholinesterase) : hydrolyzes peptide bond of 
 	proteins (or acetylcholine) , 
  
 	substrate (A-CO-NH-B) + H2O	A-COOH  + H2N-B 
  
 	Asp-His-Ser = DHS 
  
 	e- movement 
  
 	Low-barrier hydrogen bond :  
  
 	e- movement 
  
 	 (same picture as previous) 
  
 	Cleavage of the 
 	peptide bond 
  
 	Release of the 
 	amino product 
  
 	 (same picture as previous) 
  
 	e- movement 
  
 	e- movement 
 	ser-substrate bond breaks 
 
 
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