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
