Enzyme Regulation Flashcards
What are cofactors?
Addition of another non-protein molecule for enzyme activity.
- organic/inorganic
Two types of cofactors?
- essential ions
- coenzymes
What are the two classes of essential ions as cofactors?
- activator ions
- metal ions of metallo-enzymes
What are activator ions?
Metal or non-metal ions that
- bind to enzymes
- increase their activity
What are metallo-enzymes?
Enzymes that require a metal ion as a cofactor to catalyze a biochemical reaction.
How do activator ions function as cofactors?
Works by:
- stabilizing the E-S complex
- enhancing the binding of substrate molecules
- inducing a conformational change in the enzyme that makes it more catalytically active
How do metal ions of metallo-enzymes function as cofactors?
Participate directly in catalysis by serving as the active site
How do metal activated enzymes function as cofactors?
- stimulated by addition of metal ions
e.g. Mg2+
What is Mg2+ used in as a cofactor?
Glycolysis
- in 1st step of converting glucose to glucose 6-phosphate
What are the two classes of coenzymes as cofactors?
- co-substrates
- prosthetic groups
What are co-substrates?
Small molecules that participate in a biochemical reaction as a reactant but are not consumed in the reaction.
What are prosthetic groups?
Non-protein molecules that are tightly bound to enzymes and help them catalyze a reaction.
How do co-substrates function as coenzymes?
- altered in reaction
- regenerate to original structure in next reaction
- disassociated from active site
- shuttle chemical groups among different enzyme reactions
How do prosthetic groups function as coenzymes?
- directly participates in catalytic activity
- provides specific shape to enzyme’s AS
- stabilise intermediates or transition states
- facilitate electron transfer
What do co-substrates and prosthetic groups supply to amino acid side chains?
Reactive groups not present on amino acid side chains.
Summarise the classes of cofactors in a diagram
silde 11
What is the main clinical symptom caused by the malfunction of enzymes?
Dietary vitamin insufficiency
What does dietary vitamin insufficiency lead to?
Lack of sufficient cofactors derived from vitamins to maintain homeostasis.
Why does enzyme activity have to be regulated?
- prevent the stability of cells with their surroundings (maintain homeostasis)
- allow cellular events to be optimised according to need (to respond to changing conditions)
- increase/decrease the amount of enzyme (to ensure the appropriate level of enzyme activity)
- alter the catalytic properties of an existing enzyme (to prevent wasteful reactions)
Effect of temperature on catalysis
- increasing temp increases rate of reaction
- increases V0
What is denaturation?
- complete loss of catalytic activity
- due to protein unfolding (loses its 3-D structure)
- caused by change in environment (e.g. temp, pH)
What is conformal change?
- change in the 3D shape of an enzyme
- due to binding of a substrate or other ligand
- has different ΔG values
Effects of pH on catalysis
Enzymes have an optimal pH range for maximum activity:
- pH deviates too much from optimal range, E = denatured
Changes in pH leads to:
- charges on amino acid residues in AS also changing
- competitive inhibitors binding to AS
- covalent modifications of E
How does pH have an effect on substrates?
Affects:
- ionisation state → affects ability to bind to active site
- solubility of the S → impacts its availability to the enzyme
- stability of S → leads to degradation of S or formation of unwanted side Ps
What is the ionization state of an amino acid side chain?
Refers to whether the side chain is charged or uncharged
What happens when there are changes in the ionisation state of an amino acid side chain?
- alters Vmax if the side chain is involved in the catalytic mechanism
- affects protein (E) structure & function
How does the ionization state of an amino acid side chain affect protein function?
Changes in the ionization state of amino acid side chain:
- alters the protein’s (E) ability to bind to other molecules
- or catalyze chemical reactions
What are inhibitors?
- molecule that binds to an enzyme
- interferes with its activity - reduces or eliminates completely
What do inhibitors prevent?
Prevent
- formation of ES complex
- ES breakdown to E + P
Are inhibitors reversible?
Reversible or irreversible
How do inhibitors bind to enzymes?
Covalent bonds (irreversible)
How do reversible inhibitors bind to enzymes?
Non-covalent interactions
How can inhibition be identified?
Michaelis-Menten plot
What are the three common types of reversible enzyme inhibition?
- competitive
- non-competitive
- uncompetitive
What is Competitive Inhibition?
Molecules similar in structure to substrate competes with the substrate for the active site
How does Competitive Inhibition effect Vmax and Km?
- increases Km without effecting Vmax
What is Non-Competitive Inhibition?
Inhibitor molecule binds to a site on enzyme different from AS
How does non-Competitive Inhibition effect Vmax and Km?
- reduces Vmax
- Km remains same as inhibitor doesn’t affect binding of S to AS
How does non-Competitive Inhibition alter enzymes?
- alters conformation of enzyme’s structure
- reduce the enzyme’s activity
- or prevent it from functioning altogether
Why are non-Competitive Inhibition preferable to competitive inhibitors?
- do not compete with S for binding to AS
- ∴ less effected by changes in [S]
- inhibition caused by inhibitor persist at high [S] (not overcome by high [S])
What is Uncompetitive Inhibition?
- inhibitor binds to ES complex
- forming a ternary complex
How does uncompetitive Inhibition work?
- binds to the ES complex
- prevents ES from releasing P & regenerating enzyme
- removes E from reaction
How does uncompetitive Inhibition effect Vmax and Km?
- lowers both Vmax and Km
- ratio of Km/Vmax remains same
How does covalent inhibition function?
Reduces concentration of the active enzyme by:
- irreversibly modifying the enzyme’s AS
- hence decreases rate of reaction
How does irreversible inhibition work?
Binds to enzyme to alter it’s binding site
- prevents S from binding
- removes E from reaction
- & permanent inactivation of E
Effect of irreversible inhibition on Km and Vmax?
- lowers both Vmax and Km
- ratio of Km/Vmax remains same
What triggers dysregulation of enzymes?
- pathogenic agents
- genetic mutations
leads to diseases
What control mechanisms are used for enzyme regulation in the body?
- course control
- fine control
What is course control?
- involves regulating the overall rate of a metabolic pathway or enzyme system
- through the activation or inhibition of key enzymes
What mechanism is used to achieve course control?
control of enzyme quantity
What factors affect control of enzyme quantity?
- altering rate of E synthesis & degradation
- induction
- repression
- S, metal ion and coenzyme
What is Fine Control?
Altering the catalytic efficiency of the enzyme
(reversible changes in the enzyme’s conformation)
What is catalytic efficiency affected by?
- allosteric regulation
- feedback inhibition
- proenzyme (zymogen)
- covalent modification
- protein - protein interaction
What is Allosteric Regulation?
Binding of a molecule at a site other than the catalytic active site.
- reversible
- non-covalent
What are Proenzymes?
Inactive enzymes that require activation, existing as:
- zymogens
- proproteins
What is Covalent Modification?
Common regulatory mechanism
- reversible modification of an enzyme
What is Tay-Sach’s Disease?
Genetic metabolic disorder affecting the NS:
- caused by deficiency of enzyme hexosaminidase A
- results in failure to process lipid (GM2 ganglioside) that accumulates in brain + tissues
How does Tay-Sach’s Disease develop?
Infants not developing normally
- decreased muscle tone
- increased startle response
progresses to:
- paralysis
- delayed mental + social development
- deafness
- blindness
- seizures
- death
What is Chronic Inflammation?
Long-term inflammatory response
- occurs when the body’s immune system attempts to eliminate harmful stimuli
- but is unable to do so effectively
How does chronic inflammation affect enzyme regulation?
Disrupt regulatory mechanisms such as:
- cofactors
- inhibitors
- feedback mechanisms
What are NSAIDs?
Non-Steroidal Anti-Inflammatory Drugs
- medications commonly used to reduce pain, fever, and inflammation
How do NSAIDs work?
Inhibiting the activity of cyclooxygenase (COX-2)
- an enzyme involved in production of prostaglandins
- prostaglandins contribute to pain & inflammation
What type of inhibitor is NSAIDs?
Competitive inhibitor
What are the types of NSAIDs?
- aspirin
- ibuprofen
- naproxen
- diclofenac
What are the clinical uses of NSAIDS
treats:
- analgesia
- inflammation
- antipyresis
- anti-platelet effect
- cancer preventive agents
What are the adverse effects of NSAIDS
- gastrointestinal effects
- disturbance of renal function
- inhibition of platelet aggregation
- central symptoms
How do enzymes correlate to tissue damage?
Elevated enzyme levels indicates tissue damage
How are enzymes used in diagnostics?
By measuring elevated enzyme levels as they indicate tissue damage
How do enzymes indicate damage to a specific tissue?
Presence of increased levels of particular enzymes in plasma
E.g. AMS = damage in salivary glands
