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· The four classes of enzymes: __(4)__
· Each class catalyzes the reactions that require __. The mechanisms of these enzymes have been revealed through the use of incisive experimental probes, including the techniques of __ and __
serine proteases, carbonic anhydrases, restriction endonucleases, and myosins
the addition of water to a substrate
protein structure determination and site-directed mutagenesis
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· Each develops strategies to solve a certain problem:
1) serine proteases
o Serine proteases: the challenge is to promote a reaction that is almost immeasurably slow at neutral pH in the absence of a catalyst
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· Each develops strategies to solve a certain problem:
2) carbonic anhydrases
o Carbonic anhydrases: the challenge is to achieve a high absolute rate of reaction, suitable for integration with other rapid physiological processes
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· Each develops strategies to solve a certain problem:
3) restriction endonucleases
o Restriction endonucleases: the challenge is to attain a high degree of specificity
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· Each develops strategies to solve a certain problem:
4) myosins
o Myosins: the challenge is to utilize the free energy associated with the hydrolysis of ATP to drive other processes
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· These groups are families; and class members have evolved and been refined
· Binding energy serves two purposes:
What are the two?
- o It establishes substrate specificity and increases catalytic efficiency
- o It also promotes structural changes in both the enzyme and the substrate that facilitate catalysis, called induced fit
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Establishment of substrate specificity
§ Only the__ can participate in most/all of the interactions with the enzyme and thus __, accounting for the exquisite substrate specificity exhibited by many enzymes
§ the full complement of such interactions is formed only when the __ is __
· interactions between enzyme and substrate __, lowering the __
- correct substrate
- maximize binding energy
- combo of enzyme and substrate
- in the transition state
- stabilize the transition state
- free energy of activation
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· Enzymes employ one or more strategies for catalyzing specific reactions
What are the strategies?
covalent catalysis
general acid-base catalysis
catalysis by approximation
metal ion catalysis
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Covalent catalysis
o active site has the reactive group (usually a nucleophile), that becomes temporarily covalently attached to a part of the substrate in the course of catalysis
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o General acid-base catalysis: __
a molecule other than water plays the role of a proton donor or acceptor
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Catalysis by approximation
o many reactions include two distinct substrates, including all four classes of hydrolases. In such cases, the reaction rate may be considerably enhanced by bringing the two substrates together along a single binding surface on an enzyme
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Metal ion catalysis: o metal ions function catalytically in several ways. What are the three?
- § A metal ion can facilitate formation of nucleophiles by direct coordination
- § It can serve as an electrophile, stabilizing a negative charge on a reaction intermediate
- § Can serve as a bridge between enzyme and substrate, increasing the binding energy and holding the substrate in a conformation appropriate for catalysis
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