Enzyme Kinetics 3 Flashcards
What is the Active Site ?
The active site is the region that binds the substrates (& cofactors if any)
What does the active site contain ?
It contains the residues that directly participate in the making & breaking of bonds (these residues are called catalytic groups)
What does the interaction of the enzyme and substrate at the active site promote ?
It promotes the formation of the transition state
The active site is the region that most directly lowers ?
ΔG‡ of the reaction - resulting in rate enhancement of the reaction
The active site is a ?
A 3-dimensional cleft formed by groups that come from different parts of the amino acid sequence
The active site takes up ?
A relatively small part of the total volume of an enzyme. Why are enzymes so big? Scaffolding, regulatory sites, interaction sites for other proteins, & channels
Active sites are ?
Clefts or crevices -
exclude H2O
Substrates are bound to ?
Enzymes by multiple weak attractions (electrostatic interactions, hydrogen bonds, Van der Waals forces, & hydrophobic interactions can be Involved)
The specificity of binding depends on ?
The precisely defined arrangement of atoms at the active site
The specificity of an enzyme is due ? This is a result of ?
To the precise interaction of substrate with the enzyme. The intricate three-dimensional structure of the enzyme protein
DIPF (nerve gas) reacts ?
With Ser in acetylcholinesterase
Alanine non-competitively inhibits ?
Pyruvate kinase
Alanine is one product of a series of enzyme-catalyzed reactions, the first step of which is catalyzed by Alanine is one product of a series of enzyme-catalyzed reactions, the first step of which is catalyzed by ?
Phosphenol kinase
Apoenzyme + cofactor =
Holoenzyme
Cofactors often derived from?
Vitamins
When tightly bound to enzyme, cofactor =
Prosthetic group
4-hydroxyproline required in?
Collagen (connective tissue in vertebrates)
Scurvy from ?
Ascorbate deficiency
Enzyme has tightly bound Fe2+ ion, which reacts with O2 to form ?
Oxidised iron complex, which inactivates enzyme
Ascorbate rescues enzyme by ?
Reducing the ferric ion
What is Cooperativity ?
Enzyme can bind two substrate molecules at different binding sites. Binding at one site affects the affinity for the other.
Usually, the binding of the first S changes the rate at ?
Which the second S binds.
If the binding rate of the second S is increased, it’s ?
Positive cooperativity
If the binding rate of the second S is decreased, it’s?
Negative cooperativity
Give details about Allostery?
- Modulation of protein activity(enzymeorcarrier protein) by an EFFECTOR molecule.
- REGULATORY SITE is separate from the active site
- Enzyme exists in two states-tense and relaxed. Binding of the effector influences further binding of substrate
Alanine is an allosteric inhibitor of ?
Pyruvate kinase
What are the steps for extraction of energy from food ?
Stage 1 = Depolymerisation
Stage 2 = Glycolysis
Stage 3 = TCA cycle and oxidative and phosphorylation
What is Hexokinase ?
A highly regulated enzyme
What does Hexokinase catalyse ?
First step of glycolysis
How does Hexokinase work? Also, allosterically inhibited ?
Works by induced fit: a conformational change in the enzyme occurs upon binding to its substrate.
It’s inhibited by product
Hexokinase and glucokinase conduct the same reaction, but ?
Have different properties
Hexokinase is found in and is what ?
In the brain and in skeletal muscle, and is a regulatory enzyme (i.e. it is inhibited by high concentrations of its product).
Hexokinase also has a higher affinity for ?
For glucose, with a Km value of 5 X 10-5 M
Glucokinase is found in and absent from ?
Glucokinase is found in the liver, and is absent in brain and muscle
What is Glucokinase and has a lower affinity for ?
It is non-regulatory, and has a lower affinity for
glucose (Km = 2 X 10-2 M)
At normal blood glucose, hexokinase is operating at ?
Near Vmax, ensuring that the brain gets an ample supply of glucose
Glucokinase is operating far below its ?
Vmax under these conditions
If blood glucose rises significantly, hexokinase can? what does this result in ?
Speed up slightly, but glucokinase speeds up dramatically. Therefore: excess blood glucose is taken up by the liver, and converted to glycogen and fat.
If blood glucose falls below normal, hexokinase is ?
Still operating near Vmax, while glucokinase is essentially inactive. In this way, a constant supply of glucose is ensured for the brain at all times.
