Lecture 3: Enzymes
Properties of Enzymes
Definition: Protein catalysts that speed up the velocity of a chemical reaction
Properties Explanation
1) They possess active sites - Enzymes have active sites made of amino acids
on them so they can bind to substrates (bc it
makes them have a complementary surface to the
substrate)
- Active site + substrate bound = enzyme-substrate
complex (E-S complex)
2) They display catalytic efficiency - Enzymes will decrease the energy barrier for the
reaction to occur (most likely)
- The catalyzed reaction = 103 to 108 times faster
than an uncatalyzed reaction
- Turnover #: Number of substrates converted to
products using one enzyme (in one second time)
3) They display high specificity - Enzymes = very specific
- They interact with one or very few substrates
- They catalyze only one type of chemical reaction
2 types of specificity:
1. Lock and Key:
- Enzyme + substrate = perfectly
complementary
2. Conformational Change:
- Enzyme + substrate bind =
modification in the enzyme shape
- Enzymes can discriminate between the L and D
forms (isomers) of molecules
- Humans can only deal with the L form
4) Some rely on cofactors or coenzymes - Cofactor= non-protein molecule
- Function= activate enzymes by altering their
binding activity by changing their active site’s
shape and charge distribution in order to catalyze
reactions
, 2 types of cofactors:
1. Inorganic metal ions (Calcium + Iron)
2. Organic compounds (coenzymes)
-cofactors= vitamins (B in particular)
5) Their catalytic power is regulated - Phosphorylation is an example of how to regulate
the catalytic power of an enzyme
6) They are compartmentalized - Enzymes are kept in specific places inside a cell
to help them work better
- Enzymes are localized in specific organelles
- Serves to isolate the reaction substrate or product
from other competing reactions
Ex: some enzymes work better in different
conditions/environments within the body like pepsin
(works in low PH)
Types of Cofactors/Coenzymes:
Definition
Apoenzyme - Polypeptide/protein part of the enzyme
- Inactive
Holoenzyme - Enzyme with its coenzyme
- Active
Prosthetic Group - Coenzyme tightly bound to the enzyme at all times
Second Substrate - Coenzyme that binds to the enzyme at the same time as the
substrate
,Factors Affecting Rates (Velocity) of Enzymatic Reactions:
Relationship
1) Substrate Concentration ↑ substrate concentration = ↑ velocity of rxn (but up to a
certain point)
Hyperbolic relationship
Vmax= the maximum velocity of reaction that uses an enzyme
(when the substrate is completely saturated)
Michaelis constant (Km):
The substrate concentration needed to achieve ½ of the max
velocity of an enzymatic reaction
a) Low Km= substrate has a greater affinity with its enzyme =
enzyme needs very little substrate to reach ½ Vmax (desired
velocity)
Ex: Enzymes within the brain
- Have a very low Km
- The brain needs glucose to survive even when blood sugar is
low, thus a low Km in the brain can allow for metabolic
reactions with glucose to feed the brain.
- We can get away with low blood sugar (low glucose) due to
this low Km because you need very little substrate (glucose) to
achieve ½ Vmax = reaction will occur faster
b) High Km= substrate has a little affinity with its enzyme =
enzyme needs high amounts of substrate to reach ½ Vmax
(desired velocity)
Ex: Liver enzymes have a high Km
- For glucose to be stored in the liver, it must be in abundance
in the blood, thus the liver has a high Km
- It needs high amounts of glucose for the enzymatic reaction
to be stimulated
2) PH - Optimal pH for enzymes can differ
Ex:
- pepsin working in the stomach (low pH) has an optimal pH of
2
, - When low pH/high pH is not a favourable condition for an
enzyme = it will denature
Ex: during exercise = low pH due to accumulation of lactic acid
= exercise induced acidosis = if not favorable for enzyme it will
denature
3) Temperature - ↑ Temperature= high enzyme reaction velocity (rate) only to a
certain point
- Extreme temp = denaturation of enzyme
Ex: ice bath after workout
- Cold= impairs your glycogen resynthesis after you
depleted all you glycogen (not good bcs you have no
glucose/glycogen for energy)
4) Enzyme Concentration - ↑ enzyme concentration = ↑ total number of active sites = ↑
reaction rate = ↑ Vmax
BUT NOT ↑ Km
- the amount of substrate needed to reach ½ Vmax does not
change, your Vmax is the only thing changing (how fast the
reaction occurs)
5) Ionic Strength - Ionic strength = sum of concentrations of all ions in a solution
- ions can interact with diff PRO, thus they can change from
secondary to tertiary structures = affects enzymatic activity
Enzyme Regulation:
- Enzyme activity can be activated or inhibited through these processes:
Regulations: Explanation
1) Allosteric Regulation 1. Allosteric effector
- Small molecule/ligand that binds the
allosteric sites (site other than active
site).
2. This alters the shape and charge of the
active site of the allosteric enzyme.
3.
a) If the allosteric effector is positive =
the affinity of the enzyme for its
Properties of Enzymes
Definition: Protein catalysts that speed up the velocity of a chemical reaction
Properties Explanation
1) They possess active sites - Enzymes have active sites made of amino acids
on them so they can bind to substrates (bc it
makes them have a complementary surface to the
substrate)
- Active site + substrate bound = enzyme-substrate
complex (E-S complex)
2) They display catalytic efficiency - Enzymes will decrease the energy barrier for the
reaction to occur (most likely)
- The catalyzed reaction = 103 to 108 times faster
than an uncatalyzed reaction
- Turnover #: Number of substrates converted to
products using one enzyme (in one second time)
3) They display high specificity - Enzymes = very specific
- They interact with one or very few substrates
- They catalyze only one type of chemical reaction
2 types of specificity:
1. Lock and Key:
- Enzyme + substrate = perfectly
complementary
2. Conformational Change:
- Enzyme + substrate bind =
modification in the enzyme shape
- Enzymes can discriminate between the L and D
forms (isomers) of molecules
- Humans can only deal with the L form
4) Some rely on cofactors or coenzymes - Cofactor= non-protein molecule
- Function= activate enzymes by altering their
binding activity by changing their active site’s
shape and charge distribution in order to catalyze
reactions
, 2 types of cofactors:
1. Inorganic metal ions (Calcium + Iron)
2. Organic compounds (coenzymes)
-cofactors= vitamins (B in particular)
5) Their catalytic power is regulated - Phosphorylation is an example of how to regulate
the catalytic power of an enzyme
6) They are compartmentalized - Enzymes are kept in specific places inside a cell
to help them work better
- Enzymes are localized in specific organelles
- Serves to isolate the reaction substrate or product
from other competing reactions
Ex: some enzymes work better in different
conditions/environments within the body like pepsin
(works in low PH)
Types of Cofactors/Coenzymes:
Definition
Apoenzyme - Polypeptide/protein part of the enzyme
- Inactive
Holoenzyme - Enzyme with its coenzyme
- Active
Prosthetic Group - Coenzyme tightly bound to the enzyme at all times
Second Substrate - Coenzyme that binds to the enzyme at the same time as the
substrate
,Factors Affecting Rates (Velocity) of Enzymatic Reactions:
Relationship
1) Substrate Concentration ↑ substrate concentration = ↑ velocity of rxn (but up to a
certain point)
Hyperbolic relationship
Vmax= the maximum velocity of reaction that uses an enzyme
(when the substrate is completely saturated)
Michaelis constant (Km):
The substrate concentration needed to achieve ½ of the max
velocity of an enzymatic reaction
a) Low Km= substrate has a greater affinity with its enzyme =
enzyme needs very little substrate to reach ½ Vmax (desired
velocity)
Ex: Enzymes within the brain
- Have a very low Km
- The brain needs glucose to survive even when blood sugar is
low, thus a low Km in the brain can allow for metabolic
reactions with glucose to feed the brain.
- We can get away with low blood sugar (low glucose) due to
this low Km because you need very little substrate (glucose) to
achieve ½ Vmax = reaction will occur faster
b) High Km= substrate has a little affinity with its enzyme =
enzyme needs high amounts of substrate to reach ½ Vmax
(desired velocity)
Ex: Liver enzymes have a high Km
- For glucose to be stored in the liver, it must be in abundance
in the blood, thus the liver has a high Km
- It needs high amounts of glucose for the enzymatic reaction
to be stimulated
2) PH - Optimal pH for enzymes can differ
Ex:
- pepsin working in the stomach (low pH) has an optimal pH of
2
, - When low pH/high pH is not a favourable condition for an
enzyme = it will denature
Ex: during exercise = low pH due to accumulation of lactic acid
= exercise induced acidosis = if not favorable for enzyme it will
denature
3) Temperature - ↑ Temperature= high enzyme reaction velocity (rate) only to a
certain point
- Extreme temp = denaturation of enzyme
Ex: ice bath after workout
- Cold= impairs your glycogen resynthesis after you
depleted all you glycogen (not good bcs you have no
glucose/glycogen for energy)
4) Enzyme Concentration - ↑ enzyme concentration = ↑ total number of active sites = ↑
reaction rate = ↑ Vmax
BUT NOT ↑ Km
- the amount of substrate needed to reach ½ Vmax does not
change, your Vmax is the only thing changing (how fast the
reaction occurs)
5) Ionic Strength - Ionic strength = sum of concentrations of all ions in a solution
- ions can interact with diff PRO, thus they can change from
secondary to tertiary structures = affects enzymatic activity
Enzyme Regulation:
- Enzyme activity can be activated or inhibited through these processes:
Regulations: Explanation
1) Allosteric Regulation 1. Allosteric effector
- Small molecule/ligand that binds the
allosteric sites (site other than active
site).
2. This alters the shape and charge of the
active site of the allosteric enzyme.
3.
a) If the allosteric effector is positive =
the affinity of the enzyme for its
