Enzyme Kinetics Flashcards
What is enzyme kinetics ?
The study of the rates of enzyme catalysed reactions
What is measured in enzyme kinetics ?
The reaction rate is measured and the effects of varying the conditions of the reactions investigated
What does studying enzyme kinetics reveal ?
- The catalytic mechanism of an enzyme
- The enzymes role in metabolism
- How the enzyme activity is controlled
- How a drug or poison might inhibit the enzyme
What type of relationship is there between the rate of an enzyme catalysed reaction and the concentration of substrate at a fixed concentration of enzyme ?
Hyperbolic relationship
At low substrate concentrations what happens to the rate of reaction with increasing substrate concentration ?
Steep increase
What is the rate at which product can be formed limited by ?
The concentration of the substrate available
What is the initial rate of the enzyme-catalysed reaction to the concentration of substrate ?
Directly proportional
What is a first order reaction ?
The steep increase at the beginning of the curve
What happens to the enzyme as the concentration of the substrate increases ?
The enzyme becomes saturated with substrate
What happens as soon as the catalytic site is empty ?
More substrate is available to bind and undergo reaction
What happens at the high concentrations of substrate while the substrate continues to increase ?
Decreased enzyme response
When is the maximum velocity achieved ?
At substrate saturation
What is a zero order reaction ?
Proceeds at a constant rate
At maximum velocity, what does the rate of formation of the product depend on ?
The activity of the enzyme itself. Adding more substrate will not affect the rate of reaction to any significant effect
What is the hyperbolic relationship between substrate concentration and initial velocity also known as ?
Michaelis Menten equation
What is the michaelis constant ?
Km
What does the michaelis constant equal ?
The substrate concentration resulting in half the Vmax
What is the michaelis constant express as ?
In terms of substrate concentration in moles per litre
What is the michaelis constant independent of ?
Enzyme concentration
What does the Km value for mammalian enzymes usually fall between ?
10 micromolar to 1 minimolar
What is the dissociation constant of the enzyme substrate constant ?
Ks
What is the affinity constant of the enzyme for the substrate ?
1/Ks
What does Km provide a measure of ?
The affinity of an enzyme for the substrate
What does a large Km indicate ?
A low affinity for substrate
What does a low Km indicate ?
A high affinity for substrate
What are enzyme inhibitors ?
Molecules that interact in some way with the enzyme to prevent it from working in its normal manner
What are enzyme inhibitors normally ?
Poisons and drugs
What is a competitive inhibitor ?
Competes with the substrate for binding at the enzyme active site - prevents substrate binding.
What does the competitive inhibitor have in its structure ?
A chemical structure similar to the substrate
How is an enzyme inhibitor complex formed ?
A competitive inhibitor reacts reversibly with the enzyme
What is the inhibitor constant ?
Ki
What is Ki defined as ?
The dissociation constant of the enzyme inhibitor complex
What does the competitive inhibitor do to the Km value of the enzyme for substrate ?
Increases the Km- Requires a higher substrate concentration to achieve Vmax
What is uncompetitive inhibition ?
When an inhibitor binds to the enzyme substrate complex and renders the enzyme catalytically inactive
What do plots of 1/initial velocity against 1/substrate concentration measured at different concentrations of an uncompetitive inhibitor give ?
A series of parallel lines
What is non-competitive inhibition ?
Occurs when the inhibitor binds at a site different from the active site
How does binding at a site other than the active site effect enzymes ?
Reduces the enzymes ability to convert substrates into products in the active site
What happens when noncompetitive inhibitors are added into a reaction ?
The Vmax reduces as the enzyme can no longer function as well as it could in the absence of the inhibitor
Does the km for a noncompetitive inhibitor change during this reaction ?
No - stays the same
Why does the Km not change in noncompetitive inhibition ?
The enzyme can still bind the substrate but just isnt catalyzing the reaction well
