Fermentation: process by which people produce alcohol from yeast.
•Unable to reproduce using pure reagents
•Enzyme: (greek for yeast) was proposed to hint at something that catalyzes the reactions of
•Catalysts are substances that increase the rate of a chemical reaction without being consumed in
the chemical process.
•Most enzymes are proteins, but there are some RNA structures with catalytic properties.
Properties of enzymes: Cells avoid a chemical mess of functional groups that otherwise are
reactive because the rates of uncatalyzed reactions are very low.
Enzymes increase rate of reactions by 10 to 10 12 times, and can occur at much milder conditions.
Have a great speciﬁcity for their substrates and products.
Regulation: Enzymatically catalyzed reactions arer egulated by allosteric mechanisms, covalent
modiﬁcation and variation of the amount of synthesized
•Allosteric regulators: inhibitors or activators that bind to
enzyme to cause conformational changes.
Covalent modiﬁcation: phosphorylation/dephosphorylation,
particularly for receptor sensitivity.
•Gene expression of enzymes
Summary of Properties
1. Faster rate
2. Milder conditions
3. High speciﬁcity
4. Capacity for regulation
Lysase:Group elimination to form double bonds
Ligase: Bond formation coupled with ATP hydrolysis.
! Binding site for a substrate is usually located in a cleft -
pockets, gorges or crevices on the protein surface. The shape
of a substrate has a geometric complementary to the shape
of the binding site. Amino acid residues in the active site of an
enzyme are arranged to maximize favorable electrostatic
interactions with H-bonds with the corresponding substrate,
this is known as electronic compementarity.
! Enzymes may undergo certain conformational changes
upon binding of a substrate in a model known as an induced
ﬁt. Enzymes are highly speciﬁc to the conﬁguration of their
substrates, and are often stereo or regiospeciﬁc/selective.
! Certain chemical reactions are catalyzed by
corresponding enzymes only in the presents of cofactors (metal ions) or coenzymes (organic
molecules). 9 Enzymes
Catalysts reduce the activation energy of the reaction. For a 10-fold rate enhancement, a change
in free energy requires at least 5.7kJ/mol.
Curved Arrows indicate electron pair rearrangements during a chemical reaction. Arrows start at
the reactant’s electron pairs and point to the electron-deﬁcient centers that attract the electron
Catalytic Mechanism - Keto-enol tautomerization.
•Can be catalyzed by acids or bases, or left uncatalyzed. 9 Enzymes
Metal ion Catalysis
•Metal ion ensures proper orientation of substrate
•Reversible changes in oxidation state of metal ion occur
•Electron stabilization occurs, such as shielding of negative charges
•About (1/3) of all known enzymes require the presence of metal
ions in order to elicit their catalytic activity.
Covalent Catalysis: transient covalent bonds are formed with
Electrostatic catalysis: Charges on the enzyme lower the free
energy of the transient intermediate state of the substrate
Proximity and orientation effects: Substrates are brought into
contact with their catalytic groups, they are properly oriented and
enzymes freeze the translational and rotational motions of substrates
in order to keep the active groups in proximity.
Preferential binding of the transition state complex: En