Download Enzymes Activation and Deactivation

ENZYMES ACTIVATION
AND DEACTIVATION
November 19th, 2012
Enzymes are Not Consumed in Reaction

https://www.youtube.com/watch?v=0XjyAkeQJag&
feature=related
Factors Effecting Enzymes





Enzymes are not perfect
They respond to environmental conditions
They work depending on various factors which
are?
________, ___________, _____________
Changing these factors
effects? _____________
Enzyme under Stress
pH





An decrease in pH, increases the [H+] ion
concentration in solution
An increase in pH, increases the [OH-] ion
concentration in solution
These ions interfere with hydrogen bonds and ionic
bonds
Changing the conformation of the enzymes
specifically the active site
Activity of enzyme is affected
Optimal pH




Different enzymes have different optimum pHs
At optimum pH the active site is the shape most
complementary to the shape of their Substrate
At optimum pH, the rate of reaction is highest
Large changes in pH can cause
enzymes to Denature and
permanently loose their
function
Temperature Effects Enzymes


Generally, enzymes have a narrow range of
temperature they work in, Why?
At the optimal temperature enzymes are most
active
Increase Temperature
increases? energy
 Makes the substrate more active in solution. So?
 More chances of substrate colliding with active site.
 Makes the enzyme more flexible.
 Puts strain on weaker bonds.
 Pass a certain point enzymes denature. What does it
mean to denature? active site changes
 What
Decrease Temperature
 Makes
the enzyme less flexible,
 Pass a certain point enzymes do not function
properly
 Not enough energy present
Taq Polymerase





Enzyme comes from Thermus Aquaticus,
a species that thrive in hot springs and heat vents.
Functions at high temperature
Used in Polymerase Chain Reaction (PCR)
Can make multiple copies of a DNA sample using
only a small amount.
PCR can be used for a forensic investigation, genetic
diseases, drug discovery and detection
of pathogens
Temperature Curve

Various thermophillic organisms have their own type
of DNA polymerase such as Pfu Polymerase
(Pyrococcus furiosus) versus Taq Polymerase
Regulation of Temperature






Endotherms can maintain body temperature
Heat is produced and
regulated by the body, How?
Ectotherms do not maintain a body temperature
Less sensitive to changes in body temperature
Endothermic organisms are mammals, birds and
some fish
Most enzymes in the human body have an optimal
temperature of 37°C
Concentration



What is concentration?
Will the concentration of substrate the rate of
reaction?
Will the concentration of enzyme effect the rate of
reaction?
Substrate Concentration



Adding more substrate increases rate of the
reaction
More substrate molecule collide with active site
At a certain point adding more substrate has no
more effect. Enzyme active site is saturated
Enzyme Concentration



If an enzyme is saturated what can you do?
Increasing enzyme concentration, increases the rate
of reaction
Why does the graph level off?
ENZYME REGULATION
November 20th & 21st, 2012
Biochemical Process

http://www.iubmb-nicholson.org/animaps.html
Enzyme Regulation




There are enzymes for
each specific reaction
of the human body
There is a need to
control enzyme activity
Regulation is efficiency
Enzymes can be
activated and
inhibited
Road Map
Aspirin





Cyclooxygenase 2 (COX2) makes prostaglandins
These chemical are involved in inflammation
Inflammation is felt as pain and swelling in body
Aspirin reacts with the amino acid serine irreversibly,
blocking the active site, substrate can not bind
Other pain killers such as ibuprofen (Advil) bind less
strongly, are reversible bound
Inhibition






Enzyme inhibitors are substances that interfere with
catalysis
Inhibitors slow down the rate of reaction
Inhibitors can be reversible or irreversible
Irreversible inhibition – halts enzymatic reaction
permanently
Reversible inhibition – slows down the reaction
temporarily
Inhibitors can act in a competitive or non competitive
form and interfere with the reaction
Competitive Inhibition

Competitive inhibition: Enzyme inhibitors prevent
the formation of Enzyme-Substrate complexes
because they have a similar shape to the substrate
molecule.
Inhibitor
Substrate
Enzyme with Active Site Specific for
Substrate

Inhibitor Competes with Substrate
for the Active Site
Prevents enzyme from carrying out reaction it is
suited for
Competitive Inhibition





Inhibitor has a different shape than the substrate but
complements the active site
Inhibitor does not react since it has different structure
than the substrate.
Reaction rate is decreased since fewer substrate
molecules can bind to the enzyme
Inhibition is typically temporary, the inhibitor
eventually leaves the active site
Inhibition depends on the relative concentrations of
substrate and inhibitor, both compete for place in
enzyme active site
Methanol Poisoning
Methanol if ingested is oxidized to formaldehyde
and formic acid
 Attack on the optic nerve
causes blindness.
 Methanol found in engine fuel,
solvents, window cleaner, and
antifreeze

Source: http://curriculum.toxicology.wikispaces.net/2.2.5.2.5+Methanol
Ethanol Competes with Methanol




Ethanol competitively
inhibits the oxidation of
methanol by Alcohol
Dehydrogenase
Ethanol is oxidized in
preference to methanol
Oxidation of methanol
is slowed down
Toxic by-products do not
have chance to
accumulate.
Source: http://curriculum.toxicology.wikispaces.net/2.2.5.2.5+Methanol
Pennicillin





E.Coli cells
can not grow
and die
Pennicillin, an antibiotic, works against disease causing bacteria
Stops cell wall cross-linking permanently
Inactivates transpeptidase, used to build cross-linked peptidoglycan
layer in the membrane
The cross-linking peptide chains have repeats of D-Alanine
Pennicillin also has a repeat of D-Alanine-D-Alanine
Succinate Dehydrogenase Inhibitor




Succinate Dehydrogenase catalyzes the conversion of
succinate to fumerate, an important biochemical reaction in
cellular respiration.
Malonate inhibits this reaction competitively
Used to find
active site
chemistry
Used to study
inborn
errors of
metabolism
Non-Competitive Inhibition





Non-competitive inhibition: enzyme inhibitors
prevent the formation of Enzyme-Product
Complexes.
Inhibitors prevent the substrate to react and form
into product
Non-competitive inhibitors bind to a site other than
the Active Site
Binding causes conformational changes that
change the tertiary structure of the enzyme
Thus, enzyme can not catalyze reaction
Non-Competitive Inhibition
Enzyme Active Site
Complementary to
Substrate
Substrate
Non-competitive Inhibitor
Non-Competitive Reaction



Since they do not compete with substrate molecules,
non-competitive inhibitors are not affected by
substrate concentration.
Many non-competitive inhibitors are irreversible
and permanent, and effectively denature the
enzymes which they inhibit.
However, there are a lot of non-permanent and
reversible non-competitive inhibitors that are vital in
controlling metabolic functions in organisms.
Cyanide Poisoning


Another enzyme found in cellular respiration is
cytochrome oxidase, one of the most important enzymes
in the electron transport chain of reactions that occurs in
the mitochondria inner membrane
Here oxygen is reduced and 34 ATP molecules are
made.
Cyanide Poisoning






Cyanide acts as a non-competitive inhibitor for
cytochrome oxidase complex
Cyanide does not compete for the active sites of the
enzyme because it has no similarity to the substrate
cytochrome
Cyanide attaches to another site on the enzyme and
disrupts the enzyme's shape.
This brings the electron transport chain to a halt
No energy can be derived out of respiration
Hydrogen cyanide inhibits metal-containing enzymes in
the body, such as cytochrome c-oxidase, which contains
iron
Irons in Enzymes



Chemical catalyst are usually metals
Many enzymes get their ability to catalyze
reactions due to metals found in the active site
One common metal used is iron Fe2+ that is found in
a protoporphyrin ring
Ferrochelatase



Ferrochetalase inserts iron
into protoporphyrin rings
Lead forms covalent bonds
with the sulphydryl side chains
of the amino acid cysteine in the
enzyme and prevents catalytic activity
The binding of the heavy metal shows noncompetitive inhibition because the substrate still has
access.
Chymotrypsin


Chymotrypsin is an enzyme which hydrolyzes
peptides bonds
In its active site there are three amino acids
Histidine57, Serine195 and Asparagine102
known.
Hydrogen Ion Inhibits Chymotrypsin



These amino acids allow for the substrate to be
cleaved.
By lowering pH, amino acids in the active site no
longer accept hydrogen proton since Asp102
becomes protonated (hydrogens added)
Hydrogen ion acts as a non-competitive inhibitor
by preventing catalysis but do not prevent the
substrate from binding to the active site.
Biochemical Pathway




A biochemical pathway is a series of step reactions
leading to a product
Enzymes lie in biochemical pathways
There are specific enzymes for each reaction step
Metabolism is a sum of biochemical pathways and
is made of anabolic and catabolic processes
Need to Regulate



There are so many pathways that are incorporated
in the metabolic system of the human body
An efficient process is needed to regulate the use of
resources and ensure that only what is required is
being produced or broken down
Enzymes can be regulated by the ability to be
activated and deactivated when needed
Allosteric Enzyme Regulation



An allosteric site, a site away from the active site,
can bind molecules to change conformation of the
enzyme.
At the allosteric site for an inhibitor, binding of an
inhibitor causes a conformational change such that
the active sites of an enzyme are non
complementary to the substrate.
An activator can bind to its allosteric site to open or
improve the fit between substrate and enzyme.
Feedback Inhibition



In a biochemical pathway, by controlling an earlier
step, the next series of reaction steps can be
controlled
Usually the end product in a chain of reactions is an
inhibitor of an earlier enzyme in the chain to stop
the creation of more product
Process is self-regulating and cell resources are not
wasted by making more product than needed
Feedback Inhibition
Using an Allosteric Site
Regulation of Glycolysis





Glycolysis is biochemical process where glucose is
broken down to pyruvate
Pyruvate is used in mitochondria in the process of
aerobic respiration to derive ATP
Pyruvate kinase is the enzyme that converts
phosphenolpyruvate to pyruvate in glycolysis
This enzyme is the third regulated enzyme of
glycolysis
ATP and alanine act as allosteric inhibitors of
pyruvate kinase
Feedback Inhibition of Pyruvate