3.4. Hypotheses for Enzyme Catalyzed Reactions

• Many different hypotheses proposed for how enzymes catalyze reactions. However, the common link of all hypotheses is- enzyme-catalyzed reaction always initiated by the formation of an enzyme-substrate (or E•S) complex in a small cavity called the active site.

3.5. Strategies of Enzyme Catalysis

• Acid-base catalysis
  • A molecule other than water plays the role of a proton donor or acceptor.
• Covalent catalysis
  • The active site contains a reactive group, usually a powerful nucleophile that becomes temporarily covalently modified in the course of catalysis.
• Metal ion catalysis
  • Metal ions can serve as electrophilic catalyst, stabilizing negative charge on a reaction intermediate.
• Catalysis by approximation
  • In reactions that include two substrates, the rate is enhanced by bringing the two substrates together in a proper orientation.
• Proximity and orientation effects
• Preferential binding (stabilization) of the transition state