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Modes of Enzymatic Catalysis
1. _________________ modes
A. General _______________ Catalysis
B. __________________ Catalysis
2. ___________________ modes
A. ______________________ Effects
B. __________________________________
1. Chemical Modes of Catalysis
• Reaction acceleration is achieved by catalytic __________________
• A general _______ (B:) can act as a __________________________
• Can remove a proton from water and thereby generate the equivalent of OH- in neutral solution
• Can produce a stronger nucleophilic reactant (X:-)
A. General Acid-Base Catalysis
• A general ________ (BH+) can __________________
• A covalent bond may break more easily if one of its atoms is protonated (below)
B. ________________________ Catalysis
• All or part of a substrate is _________ covalently to the enzyme to form a reactive intermediate
• Can be used for ______________________________
A-X + E X-E + A
X-E + B B-X + E
Example: Sucrose phosphorylase
Step one: a glucosyl residue is transferred to enzyme
Step two: Glucose is donated to phosphate
*(Sucrose is composed of a glucose and a fructose)
2. _________________ of Enzymatic Catalysis
Binding forces utilized for catalysis – ______________________________________________________________________________
1. Charge-charge interactions2. Hydrogen bonds3. Hydrophobic interactions4. Van der Waals forces
A. The Proximity Effect - __________________________ substrate molecules in the active site
(1) Reduces their degrees of freedom
(2) Results in a ___________________________________
(3) The relative _______________________ (“effective molarity”) predicts the rate acceleration expected due to this effect
B. Transition-State (TS) Stabilization transition states bind more tightly than substrates
• The enzyme ____________________, forcing it toward TS
• An enzyme must be complementary to the TS
• Enzymes may bind their transition states _____________ times more tightly than their substrates
Transition-state (TS) __________________
• Stable compounds whose structures resemble _____________ _________________________
• 2-Phosphoglycolate, a TS analog for the enzyme triose phosphate isomerase
• Can be used medically as _______________________________
________________________ Reactions
• Enzyme rates can approach the _____________________ of the rate of diffusion of two molecules in solution
• Under physiological conditions the encounter frequency is about 108 to 109 M-1s-1
• A few enzymes have rate-determining steps that are roughly as fast as the binding of substrates to the enzymes
Triose Phosphate Isomerase (TPI)
Properties of ________________________
• Includes Trypsin, Chymotrypsin,Elastase
• Many digestive proteases similar in ________________ structure
• Chymotrypsin, trypsin and elastase - _______________ structure
• Active site substrate specificities differ due to relatively small differences in __________________________________
Serine Proteases Use Chemical and Binding Modes of Catalysis
______________ (__ amino acids) - ____ ____ ____