Lecture 10 - Enzyme kinetics Flashcards
In a reaction of the form A + B → P, rate of the reaction can be expressed in terms of:
- Rate of disappearance of one of the reactants
- Rate of appearance of the product
Overall order of a reaction is the sum total of
all exponents
A first order reaction describes a reaction whose rate depends on
the first power of the concentration of a single reactant
A second order reaction describes a reaction whose rate depends on
the product of the concentrations of two reactants
A zero-order reaction describes a reaction whose rate
is independent of the concentration of the reactant
In a zero-order reaction, the rate depends on the
presence of catalysts
Enzyme catalyzed reactions exhibit zero-order kinetics when
the reactant concentrations are so high that the enzyme is completely saturated with reactant molecules
k1
Rate constant for the formation of ES from the enzyme, E, and the substrate, S
k-1
Rate constant for the dissociation of the ES complex
k2
Rate constant for the conversion of the ES complex to product
In a steady state, the concentration of the ES complex
remains practically constant
A steady state requires equal rates for
ES generation and ES decomposition
For many enzymes, v0 varies with
substrate concentration
The relationship between v0 and substrate concentration is described by the
Michaelis-Menten equation
Km stands for
Michaelis constant
Km is the
substrate concentration at which Vmax is half
Maximum velocity (Vmax) is when
all active sites are occupied
Km describes the concentration of substrate required to
saturate the active site
The lower the Km value, the
higher the binding affinity
Turnover number (kcat) is
the number of moles of substrate that react to form product per mole of enzyme per second
The turnover number illustrates the
efficiency of enzyme catalysis
The higher the turnover number, the
more efficient the catalysis
In a Lineweaver-Burk plot, the slope of the line equals
Km/Vmax
In a Lineweaver-Burk plot, the y-intercept of the line equals
1/Vmax
In the Eadie-Hofstee equation, the reaction rate is plotted as a function of the ratio between
rate and substrate concentration
In the Hanes equation, the ratio of the ____ is plotted against ____.
initial [S]/v; [S]
Lineweaver-Burk disadvantages
- Unequal distribution of data points
- Greatest emphasis on points at low [S] (highest error)
Hanes plot disadvantages
- Unequal distribution of data points
- Greatest emphasis on points at high [S] (lower error)
Eadie-Hofstee advantage
More equal distribution of data points
