W2: Fundamental Mechanisms

by Janina S.

Name common principles and differences between chemical and enzyme catalysts!

Common principles:

increased reaction speed (Enzymes: > 10^6)
no influence on equilibrium
regeneration of the catalyst
enable reactions under milder conditions

enzyme-specific:

substrate specificity
regulation of activity
- highest efficiency possible might not be best for the cell - complex interactions
stereospecificity
dependent on environmental conditions (aq., pH,…)
higher molecular weight

Draw the reaction coordinate of an enzymatic reaction going from substrate to product via two intermediates! Indicate the free energy change of the reaction and the activation energy for the enzymatic reaction in comparison to the uncatalyzed reaction!

Name five different chemical mechanisms of enzymes!

transition state stabilization
- citrate synthase
ground state destabilization
- chorismate mutase
proximity and orientation effects
- aspartate transcarbamoylase
covalent catalysis
- lysozyme
acid-base catalysis
- RNAse A
metal ion catalysis
- carbonic anhydrase

What is the “orientation effect” in enzyme catalysis and provide an estimate for how large the rate enhancement can be in principle for an enzyme by properly orienting substrates?

collision theory: to react, molecules have to collide in the correct orientation
- enzymes can help with that
Bruice et al.: esterification reaction, reactants either free in solution or fixated in different angles towards each other
- increase in reaction speed up to 5x10^7
some enzymes exclusively work via orientation effect

Describe an example where an enzyme physically distorts its substrate with an emphasis on bond activation and energy of the substrate!

Transketolase: transfer of 2C-units between ketoses/aldoses